2000 Chevy Silverado No first and second gears

I got hit hard in the rear and the truck stopped shifting from 1st to 2nd Orig trans rebuilt at 125k and had 60k on rebuilt tranny with heavy duty parts used. Besides bumper and bed, undercarriage damage was sheared welds on exhaust. Only found bowed bands on those two low gears but the truck never shifted right immediately after the impact when tranny should have gone to 100k or maybe 120k miles still. Any suggestions why or where I can go look for answers? Thanks for listening.