Sounds like you're eliminating potential problems. I agree that cap and rotor should be replaced immediately (not the easiest things to reach). Put the new cap next to the old one and move wires one at a time to avoid getting them in the wrong order - and come to think of it, double-check that you have the wires in the right places NOW. It's darn easy to mess them up when replacing them.

Also, I would strongly counsel that you NOT engage the 4WD while having 30's on the back and 15's on the front. You could trash your transfer case too easily. Get 15's on that thing all around before you end up with a broken driveline.