I have a 2006 Expedition 5.4L with 140k miles, I have been having a issue with power loss around 3k to 4K RPMs. I have had the truck to a drivability shop who determined something may be wrong with the computer, mind you I have had no check engine light on at all. Took the truck to Ford had them flash the computer but still has no power and barely accelerates at 3k RPMs. After 4k RPMs truck actually picks up and has power again. Any ideas?

 

The CEL light may have burned out. If you have access to a code reader plug it in and see what codes are being thrown.

 

That was the first thing we did and the drivability place even checked for past codes and nothing was found.

 

I had similar symptoms on a Chevy one time and it turned out to be a couple of leaking fuel injectors. They never threw any codes either.