A buddy of mine with an '02 F250 is going thru the same kind of thing as you. 200,000 miles, the truck is not wore out, but is having A LOT of age related issues. He loves it and is determined to keep it, but he's no mechanic and between what he has been offered and what he's poured into it in just the last year would pay for more than half of a new one. I have a 2016 3500HD and feel the power, fit and finish, and upgrades are light years ahead of yours. 97 more HP and 245 lb-ft. more torque. A 6 speed tranny vs 5(?) speed, exhaust brake (an incredibly wonderful thing) stronger frame,bigger brakes and wheels. I pull a 14,000 lb fith wheel and the truck does not struggle. At all. Don't mean to demean the older trucks at all,but my opinion is, if you can afford it, get a newer one. And there are several small upgrades done over the model years you mentioned, so get as new as you can.
