I think you're safe buying a FULL size truck with high mileage. They build them much tougher than their compact-size counterparts in my opinion. I've had 3 Ford Rangers over the years and only one lasted to 200k miles...and that was the 4-banger with a five speed manual. The auto trans always go to shit in those little trucks. Anyway, as always, do your homework first. Try to find a truck that had single or maybe two owners, with solid maintenance records. Ford or GM Certified would be a good start.
This is neither here nor there, but I'm a Ford guy. I really like the F150 line of trucks. Tundras are nice too but they sure are proud of those fuggin trucks. I'm not a huge fan of Chevy trucks because the interior quality is IMO inferior to Ford's, and they seem smaller on the inside as well. GMC on the other hand seems to make a nice truck...quality seems much better than the Chevys.