If your cart is a 2001 with the forward and reverse switch by your leg it's a fleet/series cart and you have a lot of options. You don't need to do every thing at once...
First things I would do:
1 - Upgrade ALL 6 gauge cables to 4 guage...
2 - Heavy duty buss bars in the forward and reverse switch...
Those two upgrades are pretty cheap and will help a little with torque and will be needed if you decide to go with a higher amp controller. A controller upgrade will help you a lot with torque but you should to do the cables and HD buss bars first.
If you decide to go with a new controller I would get a Alltrax 500 amp for with stock motor . Alltrax also has a 650 amp controller and would be best if your going to go with a higher RPM motor in the future. I would also go with a HD White Rodgers 586 solenoid with the bigger controller.
Another option that would be cheaper is a EMP two speed motor. The EMP motor can be run in torque mode and speed mode and is switchable on the fly. I would still recommend the 4 guage cables and HD buss bars first but you can run a EMP motor without them...
If you have any questions feel free to ask and if you need help deciding on anything I mentioned or where to buy the parts we can steer you in the right direction...