Talyor Wire sells battery cables that exceed the factory requirements (size limit due to price of copper and how cheap Chevy is). I use preformed 4 gauge cables (crimped end and formed lead terminal if using post style batteries) for under the hood in my daily drivers and 0 gauge cable for battery in the trunk applications (also available in 25 foot coils) and use clamp on eyelett terminators.
The factory wiring was inadequate as to length and gauge of wire for the load. This is why I use painless wiring if I am building a race car. They custom build wiring to my needs as I specify the number of circuits along with the current carrying capacity and they size the wiring according to the fuse size and length of the wire.
In addition to heat causing resistance in wiring to increase, there is the issue of vibration and corrosion. That green roof on the courthouse is corroded copper. Because we use multi-strand wire in automotive applications (instead of a single copper wire conductor as in household applications) that increase in surface area not only increases current carrying capacity at the termination point, but it increases the risk of corrosion reducing your current carrying capacity to near zero. They use more expensive multi-strand wire to makes the wires more flexible to get it installed in a car. But that flexibility leads to work hardening of the copper (especially as the strands are small) promoting the wire strands breaking open with age from vibrations, or flexing. At a bend in the wire if it is unsupported, or connected to the motor, a large percentage of the strands may be broken only making contact intermittently.
Electrical gremlins are a pain due to diagnosing and repair are so time intensive. This is why automotive specialty shops like a stereo installation shop will remove and replace the complete harness if they do not find the problem in the first half hour of billable time. If you know basic DC circuits then a wiring diagram and test equipment and a couple of weeks of your time spent lying upside down with your head under the dash can fix anything, but it also explains why most just buy an American Automotive Wire harness to replace the aged factory wiring.