Weird trans problem, help!

[fast64]

Car is a 2001/v6/auto w/ 133k miles. Transmission started slipping real bad yesterday. Put a half quart of ATF in it and seems to shift fine now in D, 2, and 1. Only problem left is that when in reverse, the car moves forward, except for every 10 or 15 seconds it will slam into reverse for a second, then start moving forward again. Never seen something like this. Any idea what it might be or should I start looking for a transmission?

[67mustang97]

Sounds like you should start looking for a transmission. You could try a flush but that may finish it off.