2001 F 205 4x4, I have noticed on occasion that when the truck is at an incline esspecial when the front is dipping down, and you are going from drive to reverse the truck will lug down acting as if you were a manual tranny and you were starting out in the wrong gear. I replaced the stock t converter aroun 30k miles ago. It has been working fine and shifting fine, except for the occasional problem above. The fluid looks good and so does the level. any ideas.

Thanks,

 

it might be the diode in the Trans.

 

Transmission filter seal leaking (sucking air).
Transmission pump weak/scored housing.
Leaking internal seal causing pressure loss.

The torque converter clutch is held away from the friction surface by fluid pressure. Reverse in the 4R100 transmission is a hungry range. It uses a lot of fluid since there are a lot of things going on during a reverse range shifting event (just to keep the explanation simple).

You are losing fluid volume and the required pressure to keep the torque converter clutch apply from happening in reverse. Either live with it, do the cheap stuff to maybe fix it, or plan on a transmission rebuild/replace with a new pump.