Is your battery trunk mounted or in the engine bay?
Going with a bigger diameter wire is a necessity when using a trunk mounted set-up.
Also on a trunk mounted battery I run a cable from the battery all the way to the engine block.
I'd double all your grounds, make sure the battery clamp itself isnt corroded and causing a bad return to the battery, seen that cause a cable to get hot a time or two as well.
Goodluck, Cp