I ran the truck, let it sit for an hour and the volts read 12.48. Then I got into the fuse box and started pulling fuses (darn thing has 50+) When I got to 35 the volts spiked and I thought I had found something, but it was just the door and running board lights.
Nothing found on the regular fuses and nothing looked added on. There's a bunch of wiring around there, though, and the big amp under the rear seat is hot all the time. Today I'm going to check the ground for that thing, disconnect the inverter and add a couple ground straps like Tubular suggested.