Sounds like a trip to the transmission shop.
My similiar action was the lock up torque converter slipping and a new filter with a fluid change fixed it.
The general repair shop changed the filter and 3 or 4 qts. of fluid and I continued to pump out 3 qts, old and put in 3 qts new every year for 4 years....fluid is now bright red.
I don't trust the quick flush deals....1st off #1, replace the filter and whatever fluid to put the level Full on the dipstick HOT.