’04 Jeep Liberty drive line vibration while on accelerator cruising

Goof Morning,

I have a 2004 Jeep Liberty Limited, 4×4, 3.7L, automatic with 112k. I have been experiencing a vibration in the drive-line that only seams to occur when I am on the accelerator at cruising speed in 3rd and 4th gear and/or overdrive. It is most noticeable around 30mph to 60mph and is more pronounced on fresh smooth asphalt. It goes away as soon as I let my foot off of the accelerator. I have installed brand new wheels and tires and the vibration is still there. I had removed the the rear driveshaft when I replaced the rear pinion seal and in my opinion the U-Joints seamed okay, but felt really free and loose. I didn’t notice any movement in the caps or any play in the joint though. The transmission was replaced with a used unknown age or millage unit by the shady dealer I purchased it from in May. It runs and shift fine. Does anyone have an experience with Jeep Liberty’s that they could give me some advice on what to look for? Thanks!