65 BARRACUDA

Thinking Torque Converter not spinning, for about a year when I would take it out & put in reverse car would not move for 4 or 5 seconds then move. If I put it in gear have foot on brake & give it gas for 5 or so seconds the car RPM's would drop & want to stall putting load on motor. Perhaps the pump but feel tranny is issue. Need to hear thoughts.