If I were you I would look for a 2001 through 2003 Ford F350 with a 7.3 Power Stroke or a Cummins powered Dodge of the same years. With a Dodge its a crap shoot on the auto tranny. Thats why you see so many that are sticks. Same can be said with the Ford of that year range. With the Fords the 6.0 engine has a much better tranny and has been as reliable as anything out there. I would get a SRW truck and skip the 3/4 ton all together and get a 1 ton. If you get into a 6.0L Ford stay away from 2003 and 2004 models. The 2005 and later 6.0's were great but its a crap shoot on the earlier ones. That said I have a 2004 that has never been in the shop a day.
Chris
its really a shame, because the 7.3 was such a great motor, but the tranny's they're hooked to are piles of crap. the 6.0's definately had a lot of problems, but i think diamondpilot is right in that the later ones were better. i'd also agree on the 1 ton vs 3/4 - the price difference in the used market is usually very small, and the difference in build is fairly substantial.
that said, i'd include the chevy/gmc and dodge in your search. of the 99-05, i'd lean towards ford or dodge in the 99-03, but in the 04-06, i'd lean towards the chevy w/duramax/allison. the 06 chevy's forward include a 100k mile engine and trans warranty, and they have been proven reliable over the long haul. IMO, the chevy/GMC's are the best over-the-road haulers, but the least capable offroad - the independant front suspension hampers them there, and they are sprung and damped the softest. makes for the best on-road ride, but limits their capabilities offroad. they also are the quietest, a big factor in my decision to buy a chevy diesel.
i'm not brand-loyal in the least - i buy what best fits my need at the lowest cost. much like the tractors themselves, the best starting point is really defining what you want to do - dig 10' deep holes, or mow the lawn. not many machines that can do both will do either as well as a specialized machine.
ahm