Galion T500 Tranny Slip

My Galion T500 has worked faithfully for nearly a dozen years, but it has started to slip badly in the forward direction. Reverse still works just fine, but you can't get all that much done going in that direction. The transmission fluids are filled to the top of the inspection port with ATF.

I am uncertain if the problem is the transmission or the torque converter.

Some older transmissions have the an adjustment capability, but I don't think this one does.
This is a Grade-o-Matic, with...

Galion T500 Tranny Slip

Galion T500 Tranny Slip