I have a 4l65e that drives great shifts good but when I put it in reverse it binds , it will start to go back great then about 8 seconds it binds up like it has a trans brake ,go to neutral then back to reverse again 6 secs then it binds again . Any help is appreciated

 

Iwould say you have a crossleak either valve body or stator rings in pump turning on either the forward clutch or the 2-4 band

 

I had a stalled th350 that did the exact same thing. i always thought it was just debri clogging something and letting loose once it was placed back in neutral/park. but a crossleakage does sound more likely lol If i remember correctly i put a shift kit in it and maybe something happened during the install that caused it . Best of luck.