I have an ls-1 in my 51 Chevy 3100 pickup. The transmission is a 4l60e. My issue is that it seems to "strain" when in reverse. If I mash the gas it will back up, just seems sluggish. So I put the truck in reverse and took my foot off the gas and the truck will not move unless I apply the gas ?? What do you guys think? No worries ? small issue ?, No issue ? All fluids are at correct level.

 

Reverse clutches. Might post this in the auto trans section, but I'd venture a guess that it's in need of a rebuild.

Edit: I assume all forward gears are OK?

 

What does it do in foward gear? Have you driven it to see if shifts correctly? Are all the brakes free not dragging?

 

No brake issues, all forward gears are good. Truck drives fine. Reverse is the issue.