Wouldn't go without 4wd myself, though your needs may vary. With old diesels comes poor cold weather startups without use of a block heater, and the need for more warmup time, though I do enjoy diesel..
Revive your old gasser. I use this in my vehicles. As guaranteed, I've noticed quite the change in power in each engine I've put it in, and some mileage increases too.
http://shop.advanceautoparts.com/wcs...1_pri_larg.jpg