What could cause one track on a 1972 Case 450 dozer to stop pulling once the transmission gets hot?

[Mc Wyndell]

My 1972 Case 450 dozer loses pull on one track once the transmission gets hot. Low pressure drops below 40 PSI, but the torque converter pressure stays normal. Could this be a weak charge pump, leaking clutch pack, or worn spool valve issue?

 

[Nicholas Villa]

If the problem only shows up when the transmission gets hot and low pressure drops below spec, I'd start by looking at the charge pump and checking for internal leakage.