I am usually on the 6.0L section but my friend has an '01 7.3L that is exhibiting very low power (I've driven it) so low infact that when cold it won't even move...this is combined with fuel milage that has droped to 6mpg!...He was towing a 20' Ranger Bass boat but that was in I-5...freeway driving...we are baffled as is the Ford service department from two dealers, one of which I really trust...my question is it the tranny or are we looking at a turbo problem?

 

It might be that the exhaust back pressure valve is stuck restricting the exhaust gases.