I have a C4 with a reverse manual transbrakre valve body. The issue I am having is the transbrake will not hold the truck(jumps forward), and third gear is slipping. We did a line pressure test on it and the results were as follows(all readings taken Park 200 psi
Neutral 200 psi
1st 200 psi
2nd 200 psi
3rd 150 psi
In reverse if you bring the rpm up to about 2-2500 the pressure shoots to 400-450 psi, all other gears go no higher than 225 psi. Also with the transbrake engaged the pressure shoots up to 400-450 psi.
Sorry, I forgot to mention this is a fresh tranny. All new clutches,steels, and seals. It has maybe 2 miles of street driving and 3 1/8th mile passes. Found out at the track there was an issue and have not moved it since.
The pressures told you the problem. Problem is the direct clutch/cluthes/seals/rings any or all the above. Pullit back out. Check to make sure that the valve body is supposed to have that much line pressure. 200 is ok but 400? I don't think so.