Chris Richert has a good maintenance section at the 350 Diesel page, check it out at  http://members.tripod.com/~A350Diesel/trouble.html

If anyone has a diagnosing a problem I recently acquired a Buick diesel reference manual. It has troubleshooting charts, fuel system, engine mechanical, and electrical service for diesel specific components. Post at the 350 Diesel Board or e-mail me with your problem.
 

GET A MANUAL! That's an order! I've had good luck with Chiltons total car care manuals. They can answer tons of questions and keep you from screwing things up. It is the best $15.95 you'll ever spend. You could also become a member of the 6.2-6.5 dieselpage. They have info, info, and more info on your 6.2 and 6.5 diesels.
 

Oil (Thy Holy Lubrication Fluid)

    Change the oil often. Try not to let it go past 3000 miles between oil changes. Always do oil and FILTER. The reason for this is diesel combustion results in soot, and when the soot builds up enough, the particles (about 1-3 microns) glob together to around 5-8 microns, which starts to wear surfaces. Normal filters are good for bigger stuff (down to 30 to 40 microns), but soot is way to small and passes right through. That's what makes used diesel motor oil so black, so change that oil!

    If you want a better filter setup, you need to put together a bypass oil filter, where you use a partial flow, very fine (2 micron or so) filter in addition to the stock full flow filter. TheDieselPage.com has more info on how to put together a bypass oil filter setup (in the 98 reprint book). It basically means you can economically run synthetic oil because you can extent drain intervals to 3-4x as long. That way you can reap the benefits of using synthetic oil without added cost (except for the initial expenditure of the filtration setup) So hopefully I'll have some specific info of installing such a system at some future date.

    Use GOOD oil. Most oils at the auto parts store are NOT RATED FOR DIESELS! Additives in oils meant for gas engines can wacko with all the soot buildup in a diesel, you'll get sludge buildup in your engine, which is pretty icky nasty looking stuff. Your owners manual should tell you the minimum rating. Gas oils use a S_ rating (SF, SG, SJ, etc), but diesels have a C_ rating (CC, CD, CF, CF-4, CG-4). Also, if you require, say, CD, anything numerically past D is OK, like CF, but CC is not. Same goes for the gas ratings, if you need SE, SJ is OK. Oils such as Shell Rotella T and Chevron Delo are what you are looking for, and they are rated for later model gas engines too.

    Synthetics I think are a waste of money, unless you have a bypass filtration setup. They cost 4x as much, and people say you can go longer between oil changes, but you have SOOT BUILDUP, so you need to change it just as often as regular oil (except for a bypass setup). Synthetic in a gas engine....well, maybe, but you still need a bypass filtration setup to make it economical. So unless you are planning on keeping your current vehicle for over 150k, you are better off using normal oil and changing it often. If you do have a bypass filtration system so that you can extend change intervals, you should have the oil analyzed at change intervals. Synthetics are nice in that they can really reduce the wear on the engine and are easier to crank in the winter.

    As for the weight of the oil, I'd use 10W30 winter, 15W40 summer. If you are gonna run synthetic, you'll be using 5W-40 Rotella T full synthetic or Mobil Delvac 1 5W-40. If your diesel likes to leak or burn oil, stick with the thicker stuff. I know some people like to use 20W50, but the thinner it is, the quicker it flows at startup when cold, which is when much of your engine wear occurs. This is why you run thinner oil during the winter. Also, if you have thick oil during the winter, it will be hard to crank over, and you need to get over 200 rpm to start reliably and quickly. If it gets extremely cold for long periods of time where you live (like below 0F for weeks) then synthetic would be good, in a 5W40 or 0W30 weight. In my opinion, gas cars should use 5W30 winter, 10W30 summer, which is what most owners manuals say. Also go to a slightly heavier oil if you burn/leak oil.

    Oil usage is a touchy subject for some. Some people go nuts if they have to add any oil between oil changes. Oil usage can be NORMAL! If you add a quart every 3000-6000 miles, you are doing OK, especially if we are talking about a big V8. If you start using a quart every 1500-2000 miles, you might want to use slightly heavier oil. If you use a quart every 1000 miles or so, use thicker oil. If you do use that much, find out why. Is it leaking, then where is it leaking and would it be expensive to fix (such as rear main seal or oil pan gasket on a car that you have to pull the engine to take the oil pan off). In those cases, adding oil can be cheaper than fixing the problem, to a point. Burning oil is more of a concern. If you puff smoke, you've got one of a handful of problems. Worn rings, leaky valve seals, etc...

    Oil coolers are standard on most diesels, but often they are ones mounted in the radiator. Your coolant and oil will be cooler if you install an auxiliary oil cooler and disconnect the one in your radiator. The stock ones are OK, but this is better.
 

Fuel

    Try to use fuel from a reputable dealer, like truck stops that get lots of traffic. Try not to go to a station that sells a couple tanks of diesel a day. Water can get in those tanks from atmospheric and temperature changes. Most reputable dealers carry diesel with a cetane rating of 42 or better, but usually it's not listed what the rating actually is (not required like gasoline). If water is ever in the fuel system, it needs flushed out immediately. If the fuel filter is trapping the water you should probably check the fuel tank for more evidence of water. Water can kill a diesel. When water has been removed from the system, bacteria can still grow in the fuel. This bacteria was introduced by the water but can still hang out in your tank and multiply. Eventually bacteria will coat pump and injector parts and cause performance problems. The bacteria can be killed by using a biocide fuel treatment and filtering out of the fuel. Worst case the fuel system, lines, and tank must be removed and cleaned in order to eliminate all of the bacteria from the system.

    Since the quality of diesel can be in question, always run a fuel additive like Stanadyne performance formula (avail from Stanadyne dealers, they make your injector pump, like Diesel Injection Service, http://www.dieselpage.com), Power Service Diesel Supplement (avail at most wal-marts), or similar (any fuel additive must say "For Diesel Engines"). Since the early 90's, the govt. has mandated low sulfur diesel. The sulfur gave lubricity to the fuel, and fuel lubes your very expensive injector pump. It may get worse if ultra-low sulfur diesel is mandated. What the fuel additive will do is add lubricity, help prevent gelling in cold weather, some raise the cetane rating, and usually increases fuel mileage. Most have other good attributes too.
 

Glow Plugs

    Glow plugs can almost last forever, but a diesel must have a glow system in very good repair. A funky glow controller or a couple crappy glow plugs can make a diesel a bear to start, ESPECIALLY when cold. If your glow controller ever sticks, it can burn out all your glow plugs. Never use starting fluid, it can do the same. An exception is a manual glow system (toggle switch). A SMALL amount of WD40 can be used IF you heat the plugs, crank shortly, spray a LITTLE starting fluid, and crank again while the glows are still warm, but not hot. If you hear a loud pop, kick yourself in the butt and pray it didn't take out any glow plugs, and don't use that much next time. If your glow system is already half shot and you NEED to get it started, then use a LITTLE starting fluid.

Testing glow plugs - Take a multi-meter, set to ohms and zero the meter. Take power wire off glow plug, measure resistance between terminal on glow plug and a ground. It should be very low, like 1-5 ohms. If it's say 1000 ohms, it's shot. Similarly if you have a clamp on ammeter, you are looking at 8-12 amps per plug. PTC type plugs will draw less if they are already hot.

Go to the 350 diesel page for more about glow plugs and controllers, he really knows what's going on in that department. I would recommend if you have to replace a spendy glow controller, upgrade to a 85+ 6.2 diesel controller/relay. They work better and are cheaper. I have one on my buick. Also when you upgrade glow plugs, get the best, AC60G. These will not burn out like 7G and 11G plugs, and the tips won't expand and get stuck/broken off in the prechamber.There are also some glow plugs that heat up quicker but don't burn out like AC60G's, from Kennedy diesel. Check out the 6.2-6.5 dieselpage about it.

Batteries

    Battery terminals need to be cleaned periodically. Clean em up good with a wire brush every season. Use grease over the terminals to prevent corrosion buildup. Make sure all connections are tight and surfaces contact as much as possible. Use thick wires like 2 gauge or bigger for connecting the batteries up, 4ga is OK if everything is working good as is.

Intake / Exhaust
    These usually need little maintenance. You can get performance gains from porting the intake and heads and opening up the exhaust. Remember, your engine is like an air pump, easier in/out the more efficient. The more air you can let in the more fuel you can burn. Then you can turn up your injector pump for more fuel. As for the air filter, the housing could be opened up to let in more air. A good K&N filter will help out too, it's worth the $45-55 (reusable). The model 1690 is what you are looking for on most 350 diesels. 13.75"x4" The amsoil air filter sounds like it offers similar flow with better filtration. There are many oil impregnated cotton gauze filters coming out on the market, most should work just fine.