Recently rebuilt my C5 tranny that I have in a 90 Jeep behind a 302 with a Dana 20 attached to it that at the time I twin sticked. When rebuilding the tranny I replaced all seals, O-rings, clutches, bands, modulator and gaskets. Air checked both pistons and bands for operation and all worked as supposed to. Reinstalled and filled with fluid. Tranny will work as long as Jeep is on jack stands once on ground nothing but a little reverse. Dropped pan to make sure everything was lined up correct on valve body and it was. Also air checked again and can hear pistons and see bands engaging. Could really use some guidance as what it could be. I also replaced reverse servo and replaced O-rings on forward servo. Can it be valve body, modulator or torque converter? Really hoping it is something easy don't want to have to pull it out again. Any help would be appreciated.

Do you have the load set correctly on the bands.

I have done them twice just to make sure. Following what was in manual. Have went over everything that I can think of and still scratching my head.

Check out the governor assembly sounds like you have a check ball stuck in there or a broken spring.

Thanks looks like I will be pulling the tranny out.

Are you hearing any noises..like a groan or howl when engaged ?

No noises just motor. No slipping sounds are anything. Really has me baffled. As it will engage while on jack stands.