727 slipping in reverse when hot

Hi

I have a problem with 727, just like in the title it all works normal when cold, but when car gets hot, reverse slips like crazy, I need to give it 5000 rpm for the car to move at all. Can someone point me in the right direction? All forward gears work normal.
I tried swapping servos as I had aftermarket one billet one in there, I was sure it’s gasket issue, but different servo with new seal didn’t help at all. Band adjustment is also good. No signs of burning on the band as well.

Help!