I can get used to spongy, but this is way worse than anything I've experienced with this truck before. I get almost no feedback from the pedal until I'm about at the floor.
Messing with it again tonight, I pinched all 4 brake lines and got good pedal pressure. I released the clamps on the rear lines and I'd get slightly more pedal travel but no sinking. Opening up either of the front lines would result in the pedal losing pressure and sinking to the floor. I pulled the wheels and noticed a strange contact patch on the outer passenger pad where it looked like the outer 1/3 of the pad wasn't contacting the rotor enough to clean it off. Not sure what to think of that, but the driver's side looked better. I didn't really notice anything else odd with the pads, rotors or calipers. I was going to start putting old hardware back on but I realized that I already threw away my old pads.
One thing that was recommended that I've tried before is removing the vacuum going to the booster, which results in a solid pedal. I did that again tonight with the same result, but I can't wrap my head around how a failing booster would cause this issue, but I have heard people with other makes of vehicles say that it did for them. The vacuum pump is pulling 25inHg so I don't think that's the issue.