On my truck, I have a 4spd manual, with the granny low first gear. When I put the truck in reverse, if I give it too much gas, the tranny will throw itself out of reverse. I literally have to crawl in reverse. I haven't had any problems backing up a steep grade with a load, but when I have a good distance to back up, it's painfully slow. I was curious if this were a problem, or if it was normal cuz the tranny is geared so low.

 

Mine just started doing that, too. Of the 3 NP-435s I've had, this is the only one with this problem. I'm picking up another one Monday, and when it's in, I'm gonna open this one up and see why it does it. I suspect a bent shift fork.

 

Check the rear trans. mount.