Posting this on all threads:
Fixed: this was my first ever build and after reseating my gpu, I saw some less than intelligent wiring (6+2 pin coming out of my card, daisy chained to a 6 pin that then went into the VGA port on my power supply). I cringed and pulled those wires and replaced it with a PCIE cable from my wife's new build (the reason I removed my 2nd 1080 in the first place). That cable only went into a CPU slot on the power supply but didn't think much of it. Turns out using cables that are not associated with your specific PSU is a nono. Everything works fine and I am dumb for several reasons but at least I learned with (seemingly) no catastrophic consequences.
Thank yall for your help and consideration and sorry I wasted your time.
I vaguely remember ~7 years ago when I built it having issues with the gpus. The main issue was that I needed to boot my OS with a single card, get everything up and running, then shut down again and add the SLI and 2nd card. I also vaguely remember thinking the wiring was silly but it worked and for 7 years it was "if it ain't broke don't fix it" until now.
Update on my building journey: my wife's new build (waiting for 3 more case fans):