4L80E Transmission problems?

I have a 1995 Chevy 3500 dually. its RWD and it has the 7.4L motor. One time when i was driving, i tried to use the reverse and it wasnt there. It backs up on idle and if i step on the gas alot (bring the rpms up alot) then it slowly picks up speed in reverse. All my forward gears and low gears work fine. Its just reverse. Can anyone help me with this. I know about cars, just transmissions are my weak area. Thanks