89 EZGO marathon - slow speed

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Hello - I have an 89 Marathon series cart that is all stock. I have had an issue lately where the cart will sometimes be slightly jumpy/jerky when moving at speed with accelerator in a steady position. After awhile, the cart will start going only very slow (maybe half speed or less) and it will go no faster. Fully charged pack of 6V Duracells (38.4 volts) that I replaced about 1.5 months ago. No cable connections seem to be getting warm at all and all connections tight. Thinking maybe the stock controller could be going? Any suggestions on what to look for would be appreciated.

Strange part is the 4 connections on my motor are swapped S1 & S2 and A1 & A2 are connected opposite of all the wiring diagrams I can find (from where they connect to on the cart from schematic). Cart has been running this way since I got it about 2 years ago so I am figuring there may have been some variations in the past on wiring.

Thanks in advance...

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Anyone have any suggestions on how to verify if my controller has an issue with my "variable" speed results (above)? Stock series cart, 36v '89 Marathon, solid state controller.