If you can get a good cummins 95-97 are the Best , pre 24 valve , don`t worry about milage too much the drivetrain is good for approx 1,000,000 miles properly maintained , the auto trannys need to be rebuilt before that though , thye give awesome power & milage , the front ends are the weak point with poorly designed control arms & panhard & stabilizer links
Myself & a number of friends have bought diesels & we were all sceptical , but after owning them for a few weeks none of us will go back to gas , , the Cummins is awesome