I have been searching the threads for some times, with no luck. Here is my problem:
I have a 2007 F150 with 5.4L engine, 130000km.
When driving on the highway, around 60 miles/hour, if I hit a sudden bump ( let me tell you, here in Quebec, the roads are bumpy ) the transmission momentarily down shift, then return to the OD. It is felt by the sound of the engine RPM increasing, then returning to normal.
Another thing that I noticed, is that with the cruise control engaged, the transmission does not react to the road bumps. Engine RPM is constent

Where should I start ?

What is diferent with the cruise control ON ?

Any ideas are welcome

 

It's probably your foot moving on the pedal, causing a torque converter unlock and relock.

 

Thanks for the observation, this is the first thing I figured, and I tried it many times to make sure my foot was solid rock.

I got the truck for only 6 months now, and it was not behaving like this at the beginning.

 

You can't keep your foot steady on the pedal on a bumpy road. You may not be moving your foot relative to the rest of your body, but you are moving in the seat. This makes your foot move relative to the pedal.

I looked into this very issue on Superdutys. I had an instrumented vehicle where I could measure a lot of things including pedal position. While I was certain my foot was rock steady the instrumentation showed that on the bumps my whole body was moving, causing the go pedal to move quite a bit.