Electric EZGo surging under load

[jrocks1955]

1998 EZGo TXT DCS motor
I have made these "upgrades" in this order and the surging under load remains.

Alltrax controller 300. (brand new)
48 volt 650 amp solenoid
Converted golf cart to 48 volt
8- 6volt US golf cart batteries (Brand new)
D&D 502:1 motor (brand new)
Reprogrammed controller
0 gauge wiring to motor/controller and batteries.
Stock tires and suspension
Added flip seat in rear

The surging happens only under load and you can barely feel it at full speed. In other words when going up hill the golf cart surges and actually slows down. If I back off the accelorator pedal to about 1/4 throttle then the surging stops but I cant accelerate. In between each one of the upgrades I was able to drive it and the problem stayed the same. The common denominator in all this is the factory wiring harness to the controller and ignition switch and the throttle pedal. Could either of these be the problem? I Has anyone seen any problems like this? I have dumped alot of money into this cart and hate that I still have a malfunctioning cart. Any help would be appreciated.
Just so everyone knows the biggest improvements in top end speed and torque were from adding the controller/solenoid and changing to 48 volts. If I had to do it again I wouldnt buy a new motor until the stock one burns out.
With the controller and 48 volts I was radar'd at 22mph. (That is with the surging problem.)

[LostHusker]

Welcome !!!

Have you checked your micro switches? Check your ITS make sure the spacing is correct, also check your ITS. I would search your local golf cart dealers and see if you can get a used ITS if needed to check against. With everything you have done, there is only a few things left. Let us know.