I have recently rebuilt the transmission. Replaced all clutch pack plates, seals, oil pump, valve bank springs (regulator springs were broken) etc.
Once refitted and running the main pressure only stays up if the engine revs are held above 1000rpm (pressure at 135psi). If not the pressure drops to zero.
Took the engine out again and removed the oil pump for inspection. Found plastic swarf on one of the regulator valve seats that dumps oil from the pump back into the transmission housing.
Refitted pump, engine, etc. Started up and still got same problem!
When engine is held above 1000rpm gear selection and drive is perfect.
Anyone come across similar fault?