In my experience the 8awg gets quite warm at a constant 40 amps, and hotter closer to the 45 amp anderson powerpoles whose contacts are designed for 10AWG max, and the 12 awg got hot enough to be uncomfortable holding on tightly to it, but it never got stinky hot.
Fascinating...
OEM wire size for a 130 ampere alternator, 120" run is 8 AWG
It may be the shunt and connectors are using the wire conductor as a radiator.
45 amperes 3 feet length 8 ga wire should rise about 2F
Start IR shooting shunts and connectors. You cannot feel the difference of 5F but a 5F increase in a termination point is a dead giveaway the termination point is the source of heat.