Try running TDH in its ***

Thanks mrfixit,

Im going to make an extension hose for my pressure gauge so I can see easier as it warms up.

I did have a problem with the inching lever last year, the spline shaft clamp was not tight & it would not return properly, had to cut widen the clamp gap, fitted a GR8 bolt & it tightened up good. I will look close at this valve operating.

I spoke to transmission rebuilder yesterday & they advised "transmission fix" additive is only good for short term remedy by swelling seals to improve pressure.

I will check & clean the pump screen. (The line filter was pretty cruddy when I checked it (probably the first clean its had in 20 years))

One thing I wonder if ATF is available in heavier viscoscity ?

It sounds like more of a pump or pressure problem rather than the clutch plates because it is slipping in forward and reverse. Could be once the oil gets hot, and thins out, the pressure drops due to the pump. The screen that filters the oil to the pump may be just about plugged and after running a while does get plugged. Then after shutting off it clears itself a bit. Also, how about the inching valve? If it is the one mounted on the top of the transmission, they have a problem with the springs breaking. Check to see if the lever going into the trans is being pushed all the way back by the springs to engage the trans.