I think that my trans. is slipping. I have a 1998 5.4L, off road, 4x4 with 70,000 mi. on it. It has the E40D (4R100) trans.

Symptoms:
At 5,000 rpm the revs go up quickly but the truck seems to stop pulling. I put a superchip in a couple of weeks ago which raised my max rev. limit to 5,600, before it would shift at 4,900 WOT.
The engine suddenly starts to race above 5,000 rpm, at first I thaught that it was the computer starting the shift sequence, retarding timing....and so on, but now I don't know.

I put in a transgo shift kit a week ago, shifts are firmer but didn't eliminate the problem at 5,000 rpm.

All other shifts at any other throttle position are good.

Is this normal?
Any ideas?

 

I think the computer automatically shuts off the engine if you reach 5500 rpms. It might just be revving up quickly b/c you're reaching that point.