Hi I have a F250 6.0 with 90000 miles on it. At 70000 I did the minor bullet proofing. Same as you I never had a problem was just concerned. Since that time the 20000 have been heavy haulin all and over
the mountains at least four times, we live out west. I love my truck it is in great shape and it runs great.
Look for a diesel specialist in your area and go see him and ask his advice. I have heard that if the engine hasn't gone bad by a certain mileage it should be good to go. I do all other maintenance myself. Compare what someone will give you for your truck then what a new one will cost. Like others have said Most people will low ball you on the truck because its a 6.0. Peace of mind may not be cheap but new does not always mean better. Good luck in whatever you decide.