You mentioned you replaced the 80A fuse, but did you check the fusible link?? It looks like a piece of wire, and it's inline from your battery to your fusebox/igntion switch. That'd cause every problem you're talking about. Just moving it around could cause it to break...

Take a look (red arrow);

 

Hallelujah! Brothers - rejoice!!! After taking a look at my friends setup - I saw that I was missing the line off the battery (+) post straight to the 80A fusible link in the fuse box!!! Woot!

Should I run an in-line fusible link? I didn't see one on the other truck...

Who am I kidding - I'm just psyched that the thing is RUNNING STRONG!

Again - thanks so much to everyone who took the time to scratch heads with me - you guys are the best!