Only if one joint is noticeably warmer than the others then I'd worry about that, it might point to a bad connection you may need to re-make. But the cables you have are rated for 70A continuos rating, so peaking above that now and again should be ok.
The motor will pull high current if it's going uphill, so if you are going uphill a lot it might be all it is. Try it on the flat for a bit and see how it is. I took mine out for a 10 mile round trip the other night and the motor was warm to the touch, but that was coming up a long hill at the end of the trip, but as I use jump lead cable for my main power cables I've not seen an issue.
Cheers John