The other thing that might be worth looking at is the engine to chassis ground.
I’d start by cleaning the grounds and measuring the resistance of your battery cables. It should be near 0 ohms. If you need new battery cables, you could build new ones or get the big 7 battery cable kit from Jeepcables. I don’t think I’d trust parts store off the shelf ones.
If you don’t need battery cables, get the battery load tested. It may be fully charged, but it might’ve died enough that it lost some capacity.