Ok, so we towed it with a lifted 2014 F250 on 37s and went 70 with no issues on just a drop hitch with no weight distribution or sway control.
Went back and hooked mine up for a comparison. It was immediately apparent that things weren't right. The hitch has a ton of play and we noticed that my wheel wasn't staying in the middle of my wheel well. My u-bolts were finger tight.
I'll fix it and report back.
OH SHIT. Glad you caught that now. Make sure to check the center pin and all leaves for cracks, then install new U-bolts.
You have mentioned the steering box several times which makes me think you know there’s a problem there. Have you tried tightening the sector shaft? I’ve seen this make a world of differnce on a crewcab long box that you would never think would sway. Adjusting it didn’t last long, but at least it confirmed that was the problem and we replaced it.
Also do this, wouldn't hurt to reduce the sector shaft play. I like the old Toyota spec of "adjust until there's just the tiniest amount of play" which prevents over-tightening and killing the box with too much preload.