TLDR: FIXED! Replaced torque converter. Solved all issues.
I am experiencing an intermittent vibration which I believe is coming from the drive shaft. It feels like it's coming from beneath the Jeep towards the rear. I will attempt to explain the intermittence the best I can. So this vibration occurs when cruising at about 30-50-mph. I haven't noticed it on the highway yet(~70mph). When the vibration starts, I am holding my foot on the gas pedal at a static point(not attempting to accelerate or slow down). Once the vibration has started, if I immediately pull my foot off the pedal and reapply, the vibration stops... until it starts up again possibly 2minutes later or possibly never again on that drive. The vibration is loud and almost sounds as if I'm hitting rumble strips.
I have included a Google Drive link to a video I took from underneath the Jeep. The rear u-joint connection seems solid. The u-join towards the middle has a slight play in it. Wanted to check with the experts before I went and replaced the u-joint. Thank you!
https://drive.google.com/file/d/1_orCecbbZ4RkvZxdc4meINRao5DNhu__/view?usp=sharing

 

There should be zero play in a u-joint.

 

Thanks for confirming my hunch. I'll update this post once I replace the u-joint

 

You may want to check your transmission mount, engine mounts. Replace rear ujoints and verify your rear yoke is not crapped the bed.

 

Replaced u-joint at the front of the drive shaft(Connects to a black rubber boot). Still have slight bit of play. Haven't had the Jeep out long enough to experience the vibration. I'm assuming it will still be there. With such an intermittent issue, this could be a while to diagnose and fix. Thank you for the suggestions.

 

This was caused by my Torque Converter! The vibration was occuring between 4th and Overdrive when the TC was failing to lock into OD. Sounds like running over rumble strips. Replaced the TC, no more CEL, P0740, no more rumbling. Now locks into OD around 45mph and stays locked. Earned me an extra 3mpg on highway miles.