Hmmm . . . the economics of the GMs are pretty compelling. If I decide to shop for a GM, what year(s) should I look for? '92-'93 (mechanical pump) or '94 (better electronic pump)?
You may not find the economics of owning a GM diesel that compelling after you get socked for a fuel injection pump replacement (rebuilt) at ~$1500 from the stea ... dealer. But they are available for ~$1000 from other sources. There's good reason that the warranty was extended to 7 yrs/120K miles -- can you say a high failure rate. There's not much to understand there (except perhaps shades of the GM 350 diesel).
I owned a '95 K3500 6.5L TD (TurboDiesel) HO (High Output) for a relatively brief time (thankfully) about a year & half ago & I wasn't at all impressed! And I was very particular about maintenance (preventative included), fuel additives, fuel filters, etc. Even went so far as to install a relatively expensive Racor auxiliary fuel filter/water separator at ~$110. Became so disgusted with it I gave it to my brother -- that's right I gave it away!
I've done quite a bit of research on diesels & here are some other weaknesses of the 6.5L:
*Almost universally cracked heads. Vehicle operation doesn't appear to be affected tho. At least to a noticeable degree.
*One of the cylinder's is very prone to cracking. I think it's #8. Problem may be cooling related & the cooling upgrade (see below) may eliminate or significantly reduce the likelihood of occurrence.
*Vehicles prior to '97 sometimes had cooling problems, especially when towing. '97 on up went to higher volume water pump, 130gpm (vs 100?gpm), with dual thermostats. This upgrade can be retrofitted to older vehicles at a cost of something like ~$400.
*'97 on up vehicle engines were upgraded to piston cooling but original design weakened the ??? (don't remember what part of the engine) which could lead to engine failure. I'm guessing unlikely unless heavily stressed. Re-design in '98 or '99 fixed the weakness. FWIW, the Duramax was introduced in '00.
Other notes:
*The Cummins (Dodge) diesel engine is the ONLY medium duty diesel engine in a light duty truck. It's actually been de-tuned for the application.
*The 6.5L is supposedly the quietest diesel of the 3 (GM, Dodge & Ford) but I wasn't impressed. I didn't think it was much quieter than an older Dodge diesel. I can't stand noise & I'm definitely no 'dieselhead' but I can tell you that, based on what I now know about the big 3 diesel engines, I'd of gladly put up with the slightly increased noise of the Cummins (Dodge).
*Once the electronic fuel injection pump fails (& it will fail -- guar-darn-tee it) I'd definitely switch to the mechanical version as it's ~$400 less rebuilt & is far more reliable. Conversion would require modifying (or replacing) throttle linkage & perhaps pump to engine interface.
*The NV4500 manual tranny was common to both Dodges & GM's from '94 on up so any negatives would apply to both. The Dodge version is slightly better with synchronized reverse. 1st gear is 'steep' at initially 6.34 then 5.61 so it's only intended for getting heavy loads moving or idling over rough/bad terrain. Weaknesses common to both installations was 5th gear nut coming off & input? (or output, can't remember) shaft damage. Usually only a concern on, I think, highly stressed vehicles.
If you do settle on a GM, I'd look for a '95 & later for the better interiors. '94 & earlier trux have a boxy/squared off driver's side dash. The '95's on up are much more nicely contoured IMO. Much more contemporary looking (if that's important). FWIW, in '96 on up vehicles the passenger side tray/cup holders was replaced with an ugly hump containing the passenger side airbag. Another FWIW, '96 & later gas vehicles are OBDII compliant but I don't know whether diesel versions were as well. I think the main advantage is better engine monitoring.
Also keep in mind that the GM diesel was also available in 1/2 tons (1500 series). A 1500 would probably offer a more comfy ride compared to a 3/4 ton or 1 ton but tradeoff is lower carrying capacity & lighter frame. I wrote "probably" bc my old K3500 (1 ton) crewcab longbed single rear wheels rode/rides better than my current vehicle, a '95 K2500 (3/4 ton) Suburban. Go figure! Actually the explanation I've read is that my old 1 ton had 2-stage rear leaf springs while my current 3/4 ton only has single-stage rear leaf springs. Whatever the reason, I can't stand the ride in my K2500 & the K3500's ride was/is soooo cushy in comparison.
You should be able to find a GM within your budget as they tend to sell for less than the Dodges. 1/2 ton, regular cabs tend to sell cheapest (applies across all makes but the diesel was only available in 3/4 & 1 tons for Dodge & Ford). Crew cabs (not available from Dodge -- at least for under $10K) with duallies bring the most. Manual tranny equipped GM diesels are pretty rare, so keep that in mind when shopping.
Good luck.
