Vehicle: 1979 Cadillac Eldorado, front wheel drive, automatic transmission

No problem when putting the car in drive or while the car is in drive.
I put the car in reverse and on its own idle the car moved backward without any problem.
I step on the gas while the car in reverse the whole car shudders and you can hear it working and the car still goes backwards just not any faster.


Rebuild the trans or scrap it, right?