Sounds more like OEM Tech, so that's where I put it.
Have you checked your driveline Cardan joints? Had a boss with similar Sx on his F-350, he ended up getting me a screw press in exchange for changing the joints (I'd shaken them, and noted that there was far too much freeplay. Lubed them and it didn't change.)
Turns out he'd ground out all of the needle rollers in all of the joints - I checked under the caps of all joints after I'd changed them (4WD - including the ones behind the wheels, I did nine joints) and I think I actually found two needles. And they were flat.
To test a Cardan joint for play: Grip the driveline to either side of the yoke/joint/knuckle, so that the joint is between your hands. Twist alternately in opposite directions (one hand clockwise one hand anticlockwise, reverse, reverse, reverse.) You should feel no play in the joint - if you do, it probably wants replacing. You can usually get a temporary reprieve from driveline noise if you lube it, but that won't last long (it will last longer if you use a heavier-bodied grease, but it will run out with operating heat sooner or later. Nothing you can do about it.)
Replacing joints can be done with a shop hydraulic press (with a ram punch and recieving blocks,) a screw press (looks like a big G clamp with a hole in the fixed anvil,) or a largish bench vise and a couple of sockets. I use a screw press - gently hold the bow in my bench vise, position it for my convenience, and pop the joints.
I can usually switch each joint out in about 10-15 minutes, once the shafts are in hand. It only takes that long because I clean and inspect the yokes while I've got them torn to bits.
