So I've always been a 12 valve guy but now am thinking of moving up to a 3rd gen truck but most of the trucks in my price range have about 270k miles on them. I don't really know much do these trucks last much longer and if so what are good things to check on them. Appreciate the help.

 

Any cummins engine will last a long time with proper maintenance. Always check for excessive blow by, check for codes, auto trans are something to be weary about.