[Tom Goldman]

Common on Powerglides with 7 or more direct clutches .
Check with your trans builder on how many discs you have and how much clearance they have.
Even with increased clearance there will still be some rocking due to the drag of so many clutches ,especially when the fluid is cold.
That's why Stock and SS cars run as few clutches as possible and run o ring segments between the plates to keep the discs from creating drag and slowing up ET, not a big issue on most .90 cars.