So you have the 5-45RFE transmission. This one has two filters, the oval shaped inlet filter and the round spin-on return filter.
The oval filter is mounted with one screw, but important is to install the filter neck seal first into the inlet of the oil pump. Push it in place with the butt end of a hamer or alike and only THEN install the filter neck into the seal. When you install this filter with the seal already placed on the filter neck, you have a very big change that sooner or later the seal will come loose and the pump will suck air instead of fluid.
Eventhough electronic problems can cause the transmission go into limp mode (3rd gear), it would still be driveable and also reverse should continue to work (completely mechanical input, no electronics)