i have a 1989 camaro 1962 327 with a 700r4 transmission. all forward gears are great but when i put it in reverse and tap the gas my rear end feels like it shakes or slips. not sure what is going on only started that after engine swap/rebuild. any help is much appreciated.

 

Rear ends don't "slip", so that's not a possibility. About the only thing about the rear that could do that, is if the pinion nut has backed off SO FAR that the pinion gets sucked into the housing SO FAR that it hits the carrier. But you'd notice an extreme amount of noise coasting in forward as well.

More likely it's your transmission.