Fortunately what you describe does not sound like a transaxle issue, assuming you have verified and changed the gearbox oil!
Sounds to be clutch system, perhaps a small amount of residual air in the hydraulics? Can you check the clearance of the pressure and friction disc while someone presses the clutch, do it both hot and cold and see if it changes, ideally you want about 0.040".
When static how easily does the shifter move through the gate? Have you checked all the shift rod linkages, u-joints and trunnion bearing?
Julian
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