Grinding/Vibration at 70 with Clutch Depressed

Hello TW Friens.

I have done some research but haven't found a thread describing my particular problem so I am creating this thread to hopefully shed some light on my Dumb@s$.

2011 Regular Cab 4wd 5 Speed
1.5in lift all around using TRD off road suspension an a Toytec AAL.

When driving at highway speeds and either no load is applied OR I depress the clutch, I get a grinding/ vibration from what I think is towards the rear of the truck. I brought it to the dealer for a 60k mile service and took a spin with one of the techs to demonstrate the issue; they mentioned that it could be the damper inside the driveshaft needing to be rebuilt, and wanted $400 to remove the rear drive shaft... so I didn't even ask about the cost for a replacement.

The strange part to me is that there is no issue when below 50mph, and so many of the described issues from others are when accelerating from a light, but mine seems to be when the driveshaft has no load and is being driven by the diff and not the trans.

Curious if any one else has had this issue and if a ECGS bushing, diff drop, carrier drop would help with this.

Thank you all!

Pic for good measure.

 

My truck (same as yours but 2012) 3" Headstrong Dakar springs, 1.5" blocks custom milled to fix the driveshaft angle. Mine does the same thing at high way speeds when I let off to coast, not so much of a vibration (maybe slight) but almost a grinding noise. Mine didn't do it until after I put in an LC Engineering Pro Clutch kit in. I had .008" turned off the flywheel to freshen the surface. However the clutch also slips in 4WD backing up in my dry driveway with zero load. So I was recently assuming the .008" wasn't enough to need flywheel shims but just enough to cause vibration/noises when coasting and slight clutch slipping??