Re: 6.2 diesel, give me good, bad, and the ugly
I have a '90 K5 with the 6.2 diesel. Overall I have been pretty pleased with it in the 6 years I have owned it. The truck was my daily driver for about 4 years but since then it has become a weekend toy and mainly just gets used on the trails.
The only problems I have had were a faulty ECM and vacuum pump, but you can't really fault the engine on either of these. It now has over 100,000 miles on the original fuel pump, injectors, and glow plugs....though I'm sure it has lost some power over the years and I would like to replace these parts, it still runs just fine. For cold starting, the only time it hasn't started in the winter was due to a bad battery. Even in sub zero mornings it has always started right up even without having it plugged in.
Power wise, it's a little slow on the street but the low end torque is great on the trail. I'm currently running 35x12.50's with 4.10 gears and it has no problem coating the sides and roof of the truck with a liberal coating of mud. I haven't checked the mileage for a long time, but on a recent off road trip it only used 12 gallons after about a 250 mile round trip on pavement and another 8 hours of trailriding.
The only modification I have done to the engine is adding dual exhaust (or rather replacing it, mine came stock with duals). I used Rino mufflers (which should be similar to Flowmasters) and they sound really good. I constantly have people say that they thought it sounded like a gas motor and can't believe its a diesel. I ran glasspacks on it before and they sounded okay, but they seemed to wear out really fast which is probably due to the soot collecting in the fiberglass packing, but it sounded similar to a gas engine with the same mufflers just a little deeper tone and a little more mellow.
The fuel filters on the newer models (not sure what year they changed) are a much better setup when changing them. It is a rectangle cartridge that clamps onto a fitting on the firewall (no tools are needed) and has a built in bleeder valve that can be opened and closed by hand. I simply attached a piece of rubber hose to it, put the end of the hose in a container with a little fuel already in it, then crank the engine over a few times, close the bleeder and it starts.
For extra performance, a turbo is the ultimate but also pricey. Opening up the air intake and exhaust makes a big difference...this also lets you turn up the fuel pump (without getting to high of exhaust temperatures).
Also, for more info, check out the 6.2-6.5 GM diesel page ( I forget the exact web address).