97 4runner auto trans problems

my runner has been sitting for the last 4 1/2 months while i was deployed and now for some reason i have no reverse. i changed the trans fluid and filter but when i put the truck in reverse its like its in neutral. then when i shift to neutral it starts creeping forward like its in drive. i really would rather not buy a whole new transmission but i have run out of ideas since i dontr know too much about auto trans.

Try flushing it. Just draining and refilling it only gets rid of a small part of the fluid.