I have a 2000 F150 5.4l 4x4. When I am going over 50 on the highway and I am in OD, if I let off the gas a couple of seconds later it feels as though the brakes come on because the truck slow down so drastically and when I give it a little gas it slams into gear. It feels as like there is a "gap" where nothing is engaged before it slams back in. This is a rebuilt tranny with less than 7K miles on it. I took it back once and they said it was the motor mounts. I had those replaced and still the same problem. I replaced the spark plugs 6K miles ago and the COPs 3K ago. There is 170K on the truck. I only drive about 8K miles a year. Any ideas would be great before I go back to the tranny place again. My warranty runs out in less than a month and I get the impression that they will do anything to put me off until it runs out and they don't have to honor it anymore.

 

The trans converter lockup may tend to be a bit noticeable depending on what was done by the shop.
It is an electrical function controlled by the computer.
.
Also not very well known is a function the computer does that you invoked by what you do with the throttle under those specific conditions.
Here s how it works; If you guickly remove throttle as you did, the TPS tells the computer you did this and can "unlock" the converter returning the converter back to just it's soft fluid coupling a 300 to 400 rpm difference.
That's the slow down mushiness you feel.
At a moment right after if you apply throttle you will see the Tach RPM rise due to the loose fluid coupling then fall back as the converter is locked again by the computer. This action is a 'timed' function by the PCM depending on the throttle position, speed and if the brake pedal is applied.
This is all normal and by intentional engineering design.
The intent of this is to help shorten the braking distance and quickness of slowdown should panic braking be needed.
With cruise control on, the brake pedal has to knock Cruise Control off vey quickly
It helps to keep from allowing the motor to keep driving the heavy vehicle in a locked up drive train condition by going to a fluid soft condition.
This feature has been in place since about 1984 at about the time electric transmission control began even in the Bronco II and Rangers.
I think your just now noticing it on a newly rebuilt transmission because all that is involved is the converter lockup function.
Good luck.

 

Thank you Bluegrass 7. I won't worry so much about it anymore.