Here is what I learned after speaking with several repair places, from cheapest to most expensive:
1) Make sure tire pressure is at max. allowed.
2) Clean the batteries; assure terminals are free of corrosion; tigten terminals; wash dirt off top of batteries
3) Check battery while on load to assure there are no weak or dead cells. Replace the one deficient battery if less than 2 to 3 years old with another good battery of similar age; replace all batteries if more than three years old.
3) Desulfate the batteries, e.g. check out "BatteryMinder" (Google "48-volt BatteryMinder"). I have not confirmed how well that works on 48-volt Club Cars, but if it does as advertised, it should increase battery performance.
4) Check accelerator linkage. One sign of the accelerator not allowing 100% of the available amps going to the motor when depressed fully to the floor is if you hear the click only after depressing it half way or more. The sooner you hear the click when you depress it, the more likely the potentiometer will reach 100% when the accelerator gets to the floor. It can be adjusted, but for me, that is for a service tech.
5) Larger diameter tires (not wheels). The larger, the faster - act as part of gearing system - up to 18% faster depending on size going from and to.
6) New or rebuilt motor - 5.5 HP. New controller if torque is an issue, e.g. going uphill.