[JohnnieB]

Drawing a lot of amps and not delivering much torque could be one of them, but a stock controller only passes about 275A, which won't overheat good high current cables and connections, even 6Ga ones.

If the current flow was 275A continuously, the nominal heating for 6Ga is about 30W per foot of cable length. For 4Ga it is about 19W per foot.

A motor that is going on ten years old, probably has a thick layer of carbon dust from the brushes throughout its interior, which reduces its efficiency, so it probably needs to be serviced, but the stock controller still limits the current flow to 275A.

To check the motor for wanted and unwanted conductivity.
With the cables removed, you should get something like 1Ω to 5Ω between the A1&A2 studs and between the S1&S2 studs, but infinite Ohms (open) between the A studs and the S studs and infinite Ohms between either A or S studs and the case.