Transmission slipping on my ford?

Changing the filter won't fix a slipping transmission. Adjusting the transmission bands might make it perform better for a while. Worn out things don't heal up. Change the fluid and filter and you'll know at least those things are right- oh, make darned sure you use the right ford transmission fluid. Put a new gasket on the pan after changing the filter if you don't want it leaking.

I'm going to guess that the loud thumping under the car is caused by the transmission mount, one of the four mounts that hold the engine and transmission to the frame.

My second guess is that when you feel the transmission slipping, it's the movement of the loose transmission pulling the linkage slightly out of gear, hence the slipping.

Only a qualified transmission specialist can determine what the problem is. Trying to guess is hopeless and you will end up going to a transmission shop anyways.

i would have to say changing the filter should help it out ! if the filter is dirty then the front pump can,t pick up the fluid fast enough !