Devilisht2003

I've searched and searched the web and forums with no success. I have a 2016 Supercrew 5.0 with 6.5ft bed and getting a pretty harsh intermittent vibration through the seats/floorboard at 80mph , steering wheel is fine. Set cruise at 80 and sometimes its smooth as glass then slowly the vibration builds, shakes a while then fades. Little while later same cycle. Currently running 2in Crown drop shackles with 4x4 block removed and Belltech adjustable struts up front dropped 2in. Wheels are 22x10 MRR T228 with 305/40/22 Grabber UHPs. Tires balanced twice and road force balanced twice. I feel the vibration with stock 20s as well but not nearly as bad. I've put in 3 degree pinion shims thinking that would help, nope. Have checked operating angles and they seem in spec. Phasing is good as well. Just for ****s I tried moving the carrier bearing down some to see if it effects it, doesn't seem to. Even played with hose clamp balance checking and no help. Any thoughts?