You really should put the tranny in neutral, jack up at least one rear wheel and have someone turn the wheel by hand slowly while you watch the teeth go by inside the hole on the tranny. If you see any damaged teeth in there, replacing just the driven gear might not fix the problem.

'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.