Rough vibrations at 45-60mph

It's a 98 4.0 ,231, d30/chrysler8.25 no lift.

I just bought two new tires in the back that match the fronts and they balanced the wheels too. I changed the diff fluid last night and during that I checked all the gears and pulled out the axles shaft. Got everything back together and it still makes the noise that it did before any of this. I went to midas last week and they said that the drum brakes were fine.

Any suggestions as to what i should do next? Im about to change out the t-case fluid and see if that affects anything. My shocks and leaf springs are in rough shape, could it just be that due to less dampening effect from the shocks that im feeling more of the vibes? Could it be the ujoint or whatever on the driveshaft? Thanks a lot and i appreciate any help.

what kind of shape are the motor and tranny mounts? I would think the tranny mount would cause the vibes....or maybe bad joints in the rear drive shaft.

I replaced one of the motor mounts and ill be installing the other one pretty soon. I think the one on the crossmember is bad too because when i hit bumps i can feel things hit my feet (prolly a mix of tcase and exhaust). I'll be ordering one of those new next week too.