We have a 1996 F350 with the 460 cid and three speed tranny. We knew the truck had a few problems when we purchased it but this one has us stumped for the moment. If the engine is set to and held at 2000 rpm after a few seconds (apx. 10) the engine will throttle back to 1500 rpm by itself.... the accelerator pedel has been kept in same physical location all the time. It is smooth running, starts easily, has no smoke in the exhaust, however the check engine light does not come on when the key is turned on or when the truck is running. The truck also has a considerable power loss as the road speed/rpm's are increased. Power 'seems' good from a standing start up to about 45 - 50 mph and then it just seems to run out of power.... if it is kicked down to 2nd gear the engine revs up but power is not there... no pre ignition just no power and the acceleration is very slow. Sort of like the feeling if the vacuum advance is not functioning in cars from 'my era'. Checked to see if there was a mass air flow sensor but didn't see one and didn't think a defective throttle position sensor should cause this type of problem.
With Kind Regards,
John

PS: one other thing that we checked was the back pressure on the CAT... it was about 1.5psi at 2000rpm.