93 Safari transmission prb

I have a 93 Safari 4.3L. It was leaking some transmission fluid so I changed the filter and replaced the Tran-pan gasket. Shortly thereafter, she stopped shifting into 3rd, 4th gears. When in D, shifting from 2nd she just revs. I can down shft into second and first, but that's it. Help!

is it doing that all the time or after youve been driving for a while like just randomly. and if so does it stop after you restart the engine if so its probibly one of the shift solenoids and the reason it stops shifting is because the transmission goes into a safety state to prevent further damage.

Have you checked for codes?
Did you use silicone sealer or other sealer on the pan gasket?
Did you get the right filter and get it installed good?
Have you checked the fluid level when hot?
MT