Sounds like the T-400 forward clutch is a problem.
Was the T-400 parts replacement job performed with a full paper and rubber kit? Sealing rings in this T-400 were metal or a teflon looking material?
Clearances on the clutch pack of this T-400 were set at what clearance?
What condition was the pump in this T-400 ? Was the side clearances of the gears checked in this T-400?
Some people are like Slinkies... Not really good for anything, but they still bring a smile to your face when you push them down a flight of stairs.