He has had a couple of EGR valves replaced already and a turbo was put on when our uncle owned the truck.
I don't know of any codes and the oil level is good.
I rode in it today and it was stange. The motor sounded fine and did not change rpm. It seemed like the trans or torqueconverter may be locking and unlocking. I don't think that it is the motor but who knows.
The strange thing is I have an 06 F250 and the only work other than normal maintenance was the fold down console broke.
His has had a new torque converter, rear main seal, turbo, and this problem has been going on since he baught it form our uncle a little less than a year ago. There is 37000 miles on the truck and I don't know about the fuel filters.
Thank you for your input and sorry so long.