you say "trans does not slip", ?is that from feel, or from taking pressure tests?
These trans don't really -feel- like they slip until the pressure is lower than about 75 PSI, but it -should- be around 150 to 175 PSI, (someone else can look up the exact numbers for us) and IS slipping the clutches at lower pressures (like riding with the operators foot resting on the inch pedal).
Disassemble the inching linkage bell-crank, and lube the shaft, so that it moves freely.