Ok so here's a good question for you guys... My truck hasn't done this for a while but I imagine it may do it again someday. I have a 2003 5.9 4x4 1500 automatic.

When cruising down the highway with the cruise control on and my foot nowhere near the pedal, every once in a while the engine RPM's will surge up slightly and back down as if the tranny were slipping or something but I don't feel any slow down or release of power.

Could it be slipping??

 

how much does it "SURGE" meaning does it go from 2200rpm to 3500rpm or is it a smaller increment than that?

 

It jumps about 500-1000 or so, I would say...

 

it is probably your torque converter locking and unlocking to go up small hills instead of downshifting it locks the torque converter clutch and the engine rpms raise a little bit to compensate for this action and it pulls you over the small hills without downshifting. or if you are in cruise it sees a deceleration and locks the converter clutch and pulls more rpm to get you to your speed preset instead of downshifting to get you there. you wont notice that much of a speed increase but it is just enough rpm to get you over the small hill or back up to where you have your cruise set so that it doesnt have to downshift.

 

That kind of makes sense but most of the time it happens is on my drive out to Sterling from Denver Colorado and it's almost completely flat. I've paid attention to whether or not there was a hill and most of the time it's happening on level ground and also no wind...?

 

...also it does it like 3 or 4 times in a row sometimes, forgot to mention that.

 

i have the same engine and tranny as you and i have never noticed it but i dont really pay attention to it so next time i take it on the highway i will see if i can feel it or notice it. i pretty sure it is your torque converter clutch. if it is your tranny slipping i am pretty sure you would know it.

 

ok so if it is then I assume thats sort of a normal thing even though it had never done it before until about a year ago (owned the truck for 4 years now) or do you think there something I should check into?

thanks for the info!

 

it might be worth taking it in to have it checked out just to make sure.

 

I'm going to be doing a bunch of tuneup stuff and all so if it does it after that I'll definitely take it in. Thanks for the help