New C4, lost forward gears after warm

Hey guys new to the forum. I just rebuilt a C4 transmission, All new seals new forward and direct drums pretty much everything is new, w/ a reverse manual valve body. Its done this twice now ill drive it for a little bit then when it warms up i lose all forward gears. I still have reverse but no foward gears. And when its cool everything works fine, good shifts no noise. Im lost can anyone help.

What valve body did you install in it?
Did you follow torque specs?

I bought the valve body from broader performance, and its a reverese manual and i followed torque specs

Time for a pressure guage see what happens when gears drop out.. Broader stuff is good gear

Sounds like a warping in the tranny somewhere causing a misdirection of fluid maybe... Only happens when it gets hot...

Im going to hook a gauge up to it today, if the main line pressure it to low then im really not sure how to figure if its the pump or maybe the valve body. I dont think its the pump because reverse is fine. So somwhere in the forward circuit..

ok so i checked the mainline presure an he it is
1st-75
2nd-65
3rd-65
N-120
R-95

Little low huh? i should have about 200, i think my pump is trashed

A serious leak somewhere can do it too. That is way low. Are those pressures when it fails or all the time?
The Broader valve bodies yes should be up around the 200 depends on how it was setup.. Last Broader Rev man i did was 220psi

he sent me the complete valve body. That is when it was failing, not extreemly hot either. But when its cold it works. If the forward clutch piston seal was shot would i lose everything or just 1st? Im pretty much lost. I have to pull the trans at this point, So i guess im going to look for

cracked forward drum
Bad piston seal in forward drum
could be the pump
could be the valve body

Forward clutch piston seal will just be no forward. Reverse will still be fine.. Low pressure all round i'd be looking at a V.B or pump issue.