What is wrong
The car will run perfectly fine until you go to stick it in gear once you put it in gear the car will
die in the battery will be dead I took the negative battery cable off and the alternator is fine
Please tell me you didn’t take the battery cable off with it running, if you did you may have damaged the computer on top of having a locked up torque converter. You need to have the battery load tested and replaced if it failed, then run a voltage drop test on the battery cables and replace them if they fail. That should take care of the start and run systems. The only fix for a locked torque converter is a new one installed and that means the transmit has to be removed.
Is vehicle an automatic or manual ?
Torque converter clutch solenoid and also not a good idea to remove battery terminal with engine running with vehicles that have computers in them can short out the computer.