[Ackattack]

I would say a 1st gen 12V cummins for max economy. They have the VE injection pump which I believe will adjust the timing, increasing fuel efficiency. The VE pump won't make as much power as the p-pumped 12V, but can still make good power.

The p-pump 12V will also get decent mileage and put out some power if you know what you're doing.

After that you get into the electronic diesels such as the 24V cummins, common rail cummins, duramax. IMHO with those engines the expense goes up and the reliability goes down. I know when I was looking at what diesel truck I wanted, I looked at earlier duramaxs and when I saw they had injector issues that required replacement at a cost of ~$2k I said no thanks. I believe the 24V have problems with thier injection pumps going out occasionally (again ~$2k).

I would avoid the 6.2L and 6.4L diesels. Just not worth the hassle. I can't say much about the powerstroke engines as they weren't a consideration for me. I think the 7.3L are OK, but there is a reason why there are a lot of "Fummins" out there.

The other part to consider is the tranny. Pretty much, stick with a tranny that came behind a diesel if you want it to live. To get an auto to live behind a hopped up diesel, you're talking big money. I went with a 5 speed mainly to avoid the auto tranny rebuild costs, though my clutch wasn't exactly cheap.

So I ended up buying a running 94 dodge 3/4t 4x4, test drove it a few months while I got a truck to put the cummins in and gathered some parts.

Good luck man, I don't think you'll be disappointed.