The pressure drop doesn't happen during first engagement. Say you start the car up in the morning, drive it around town, after its good and hot, you come to a stop light. When the light turns green you lightly touch the throttle, that is when it drops pressure, then instantly reapplies all pressure. With the engine reving and the trans basically in nuetral it will apply the FWD clutch and BAM, it hits hard. I have replaced the pump, sealing rings and the FWD drum/input shaft assembly. The seals on the FWD piston have been replaced twice suspecting a nicked or cut seal, no luck there. I don't exactly remember what happened when I hit the O/D button, under normal driving conditions(not acting up) it all works spot on. This is driving me up a wall...
Known good valve body (drove great for 100 miles then reappered)
All piston seal
Sonnax O/D pin
Reverse servo and cover
All have been replaced during rebuild...