Hard start question

[dave`12]

Put a v8 and summit headers in the truck.

Good battery (12.6 off and 13.8 running volts). New remanufactured starter with new solenoid.

Starts instantly when cool. When hot, very hard to turn over. Once it turns over, it starts quickly.

I got a heat shield wrap around the starter and the solenoid. I've tried to route the cables as far from heat as I can. The small ones going the the solenoid are also wrapped with heat reflecting wrap.

What should be my next step?

I have cheap autozone battery cables, they don't say the gauge, but I'm gonna guess 4 gauge. And the + is quite long.

Do you think going to 1 or 2 gauge should be next? Also considering header wrap, but I'ver heard bad things about that stuff.