Stay away from early Ram's, period. Yes, a Ford inline 6 will run forever if taken care of. Can't go wrong with a Chevy unless your getting a late 90's Silverado, lotta problems with the fuel pump/sender I've heard. I had a 2004 Dodge Ram I put 200,000 miles on and still drove like new, never replaced anything other than regular maintenance items and brake rotors and have a Chevy 3500 dually now with 80,000+ (got it with 32k 6 months ago) and nothing but oil changes.

But... Full size Toyota cannot be beat. My Father in-law owns a concrete company. His T100 had 485,000 miles carrying almost maximum payload capacity everyday until the differential exploded. Motor was still good but he traded it in on a new Tundra which already has 150,000 on it. Never a problem out of either aside from regular maintenance.