I would guess that the transmission is just getting old. Sometimes, when you put new fluid in an old transmission, the increased line pressure can cause the transmission and its clutches to struggle some. You might have some luck adding some Lucas Stop Slip to your transmission. I have used it many times, with a decent amount of success. It can be found at all of the chain parts stores.
Friday, May 14th, 2021 AT 11:32 AM