power loss during climb - F250 6.0 diesel
I have a 2004 F250 6.0 diesel, with 65000 miles. While towing my boat (tow-haul enabled), I experienced a significant loss of power while traveling up a 7% grade while driving at 65 mph. Normally I can maintain 65 mph on this hill, but when this occurred, my speed dropped to 30-35 mph during the last mile of the climb. Outside temp was around 90, and altitude was around 4000 ft. All gauges (oil, temp, tran temp) were normal, check-engine light did not come on, and no other symptom/indicator appeared. On the next grade, about 40 miles ahead, no problem occurred (I was able to accelerate to 80 mph). This is the first time this has happened.
Next day, I found that my oil level was one quart above full. Could this be the problem?
I have seen other posts taking about turbo problems; could this be turbo-related?
Any ideas welcome.