Only when you go WOT? or does it maintain after staying WOT?
I don't think the axle nuts could cause that but its worth a shot. I also know that the front cradle bolts are to small from Ford. They should be 9/16. I don't see that causing the issue either though. They can help contribute to wheel hop from what I've read. The only thing I would think that could cause that would be the cradle bushing are worn since the whole rear end wobbles.
I would check all of the bolts, your camber bolts, axle nuts, IRS subframe bolts should never be that loose, but if you are going to be under it and have not already done so, I would upgrade to the bigger front subframe mount bolts. I had that happen to me when a shop did an alignment and didn't tighten down the camber bolts, It was sketchy for sure!
I had that problem as well. I attributed it to my 335 Nitto's and rubber IRS bushings. I yanked the IRS and did full poly then switched to 295 tires with a stiffer sidewall. Now I don't sway