Very bad vibration on my truck?

I have a 2000 ford ranger 4x4 with a 3 inch body lift and 4:11 gear ratio swapped for my big tires… Which are 33x12.50 mud claws. Anyways, at low speeds, it is kind of an annoying vibration around my feet area. When I get over 45mph, it gets scary as hell. The vibration turns to a shaking of the entire truck. Now, it still handles perfect, and I checked the U joints and they were fine. I checked front and rear diff fluid and it was fine. I didn't see any leaks. I checked wheel bearings and they were good. I checked the CV axles for any torn boots or play and they seemed fine. I even jacked it up and spun the tires in drive with it running, and no noise. I'm lost… Maybe it's just the tires? They are very aggressive mud treads. Maybe they aren't balanced or I slung the weights off or something. I don't know. The only thing I noticed is a little more play in the rearend than I would like. I can turn the driveline a quarter turn in both directions in nuetral and wheels on the ground. Any ideas, advise, things to check next, or anything would be appreciated.

When my jeep started doing that it turned out to be the steering linkages and the stabilizer.

It's the tires, Sparky. Your heavy lug tread tires were never intended to be driven on pavement at highway speeds. I'll bet they're noisy as hell too.

You thought it would ride nice with those mods? Doesn't matter: even if the vibrations from the tires and mods were tolerable to you, they are still ripping the hell out of gears, joints and everything else… But you look so kewl in the meantime (not quite so when you're on the side of the highway loading the driveshaft.)

Always start with the simple things first. Get the tires balanced.

Only a real dummy would wonder why they have a **** ride after lifting their truck and putting large knobed meaty tires on their ride.

Could be your engine mount or your muffler

Sounds like you got 2 problems with the way it was lifted: Coil- lift kit, and cheap Body-Lift kits do not include steering system components. They also do not always come with motor mount and transmission mount shims. You wind up with the steering geometry wrong and the powertrain geometry off by just enough that there's powertrain contact with the vehicle at the firewall, or the exhaust line components are hard against the underside somewhere. With the steering linkage connected to an OEM pittman arm, vice a lift-modified "drop-down pittman arm" there's too much play in the wheel 'on-road', and there's massive bump-steer when truly 'off-road' and hitting rocks and ruts. That steering problem is potentially dangerous. The powertrain vibrating against the truck body will eventually break something, usually a motor mountor an exhaust hanger.
Take it to an Off-Road Custom Shop, put it up on a lift, get a 4X4 specialist to look it over with you, tell you what needs changing.