Failure in Transmission Thunderbird SC 1994

How are I new on this page and first of all congratulate the usefulness of it.

Now my problem is as follows, I have a Ford Thunderbird SC 1994 which for a long time has a transmission failure.

He started with a fault when braking in a stop and wanting to advance again the car felt very without strength (donkey) and melted, the change was very suddenly mentioned, it is worth mentioning that the fault only showed up in this situation, being completely stopped and lowering the parking lever to any other position did not feel any blow or something for the style or by moving forward, the changes entered in its moment and quite soft; After this fault persisted now if it began to affect the other changes, for example from first to second and so on, what was towards the changes entered very suddenly even without having stopped and in continuous acceleration

Subsequently, a workshop for a greater transmission repair, pasta, turbine and other pieces that suffered wear and breakage for sudden changes were met.
When he left the workshop, the transmission felt luxurious and there was no problem under any circumstance, but after a month he began to make exactly the same failure of before repaired.
The car returned to the workshop as a guarantee and mentioned that the valve body was cleaned since it was very dirty and I stay again without any failure but this has already been repeated four times and continues to pass, with the same diagnosis dirty valve body. The fault is only when stopping in the stops and now the reverse, without failure in the changes with constant acceleration.

My question is that it could be causing the valve body to get dirty as the workshop specialist mentions or that another cause could be.

The only other failures that I know at the engine level and that were already corrected before they failed and have not presented simultaneously is an error code in the IAC valve, the TPS and recently the EGR

The IAC valve was corrected and only the EGR and the TPS remains