Skreed

Wheeling one day I tried to recover a vechical in reverse using front tow hooks. When I started to use some force it sounded like my reverse gear started stripping / grinding. Now when I go into reverse if on flat smooth ground I'm fine, but when I give it some gas going up hill or over an obstical I get this griding sound again. Everything is fine in foward gears. I drained and replaced the fluid twice and no change. Any ideas what my opions are?

Auto tranny btw