4T60E rough 3-4 shift under light throttle

The car is a '95 riviera supercharged with 135k.
I tought to change the fluid (Royal purple) and filter. it's slightly discoloured, but dosen't smell burnt.
any suggestion?
I'll put in a trans go shift kit too.

thx!!

could be OD not working properly or a small vac. leak

thx for the quick reply: I'll give it a try.