transmission is dragging wont change gears on 1996 Chevrolet Lumina APV

i have a 1996 chevrolet lumina van, recently it was overheating come to find out the heat gasket was blown. after i got that repaired now the van can barely move, you have to push on the accelerator hard for it to move and its still dragging and will not switch gears. do i have a bad transmission or do the transmission need to be reset. there is plenty of transmission fluid in the van. thanks

Asked by for the 1996 Chevrolet Lumina APV