There seems to be some confusion here.
Is the problem that the cart won't run, or is it that the cart runs but has little power and looses speed going up hills?
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For liability reasons, disconnecting the reverse beeper isn't a good idea.
It can be toned down to a less irritating level by plugging the holes with something and taping the plug in place with electrical tape.
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How fast a series wound motor spins is dictated by the voltage applied to it and if the mechanical load increases (IE: Going up a hill), it will try to draw more amps to maintain that speed. When the amp delivery system cannot supply any more amps, the motor slows down.
With a higher amp controller, the motor won't slow as much.
Of course, the rest of the high current loop (Cables, solenoid and F/R switch) has to be capable of delivering the higher amperage.
To get a series wound motor to spin faster, more voltage is needed.