Another vibration thread

Just picked up an 07 2wd 5 lugger standard cab 4cyl auto for commuting. It's got what definitely feels like a drive line rumble/vibration. Comes in a little at 45-50 then goes away until 65 where it's much more noticeable until about 75 where it completely goes away all the way to 90 (fastest I've taken the truck). If I jack it up and run it at 75 and watch everything underneath I can't see anything vibrating enough to even tell what it could be. All wheel bearings feel tight and smooth. Pinion bearing has no play and feels smooth. I replaced both ujoints. It's a single piece driveshaft so no carrier bearing. I also replaced the trans mount (rear engine isolator?). I even went as far as getting a new driveshaft but driveshaft power Inc sent one that is completely wrong so I can't give that a shot for now. It's definitely not a tire vibration. I'm very familiar with what those feel like. If I let off the throttle when it's at it's worse so it's at a neutral power/coasting point it does let up a lot. That's why I figured ujoints but no such luck. Third member carrier bearings? It's got me at a loss. It runs smooth as glass at anything over 75.

 

Jacked it up pulled the wheels and put a couple lug nuts back on the brake drums. Still same vibration. New correct driveshaft is on the way. I guess after that next is third member if that doesn't do it. lol.