A833 - are they usually a hard box to drive?

If it shifts worse hot, there is something wrong, not necessarily in the box

Not sure if / how the clutch might be affected by hot /cold, but I would CERTAINLY check that the thing is releasing clean. Figure out "what is in there" and consult the people who made it as to release gap

PILOT BUSHING. If the bell / transmission / engine is slightly out of line, and or if the pilot is too tight or not lubricated, THAT would bind it up

I don't see poor syncros causing this worse hot rather than cold.

There's a large disagreement on ATF vs 90 wt. Some guys claim they had better luck always using ATF, some say 90wt.

I always used 90 wet in mine. I never considered a Mopar box particularly easy to shift.