Rear end vibration

I just purchased a 2008 Tacoma DCSB TRD Sport 4x4 back in December. Over the past few weeks I've started noticing a vibration coming from the back, possibly passenger side. It seems to be when I'm starting to accelerate and going anywhere from 15 to 35 mph and still accelerating. It almost feels like either the rear end is bouncing or engine is struggling. Going up hills the problem is more pronounced but it can even happen on completely flat roads. I can either slow my acceleration or really gun it and it will go away. Any ideas what this could be?

 

Check your u-joints. My bet is one or more are in need of service or replacement.

 

Replace all if doing one. Only use greaseable Spicer u joints.

 

So based on a youtube video, I got under the truck and tried to "shake" the u-joints and they didn't seem to move. Could it be something else?

 

You ever figure this out? I have a 2018 and starting to get some vibration. Still at square one so researching all ideas before I start jumping in.