Lift Pump?
 

Ok here is my situation. When I'm driving between 42-47mph and the rpms are about 1250 the engine revs up to about 1700 maybe a little bit more then back down to 1250. It happens either with or without a load and I dont think its the trans cause it doesn't feel like it shifting and speed remains constant. Also my mpg has not been what I thought I would get from a diesel.

This is my first diesel, I got it about 2 months used and I love the truck, I'm just not sure about what to check or change. I've been reading alot of the posts here and the info has been great. I have guages ready to put in, but have not had the chance yet. Any suggestions of what to change or check would be great. :)

Mike

Does this reving jump up by itself, while you are keeping the rpms (throttle) at a consistent speed? Like the engine is surging up? I'd put the gauges in ASAP just so you know where you stand fp wise.

Yes it does it by itself. At first I thought it was me moving my foot, but it has happened several times now.

Mike

It sounds like the tranny is slipping to me. When the tranny starts to slip the enigine doesn't have a load on it so it revs up in RPMs. I am just guessing, but it could be your torque converter. Just my opinion though.