No reving the motor when cold is not ok. If the transmission fluid is ok then see if the parking brake is fully disengaged. Also the transmission may need to be overhauld. My 77 Impala was needing to be reved inorder to back up. Turns out an o-ring in the gear selector shifting portion of the transmission was bad, you may have the same problem. If it is the only fix is to rebuild or replace the tranny.