69olds350

ive got a 69 cutlass 350 310 hp 350 trans, the issue im having is coming off the line, you have to push the pedel pretty much to the floor to get the car moving, but once it starts going the power and torque come in and the car takes off and runs great through the rpms, the motor dosnt seem to have ever been apart tuned to specs and throttle response is excellant in nutreal plugs are burning nice and compression is all in range, could this issue possiable be in the transmission (though trans goes in gear and shifts tight)or rearend, im having a hard time figuring this out so any help greatly appreciated thanks jeff