Being that you're at 6" in back, (leaf pulled & 3" blocks) you definitely needed to flip the carrier bearing, and give a while for the ujoints to settle into the new angle, the vibe should go away after a bit. I recommend blocks with a 1/4" (3 degree) taper. Also, on my site, when people order blocks, I encourage them to leave me a comment regarding their rear setup (like you did in your first message) so I know if the blocks need to be tapered and hole & pin offset. What I mean with hole & pin offset, is at your 6" drop, your shaft is pushed inward, so what I do for your set is I locate the hole 1/4" forward from center & the pin 1/4" back from center, which pulls your axle back 1/2" and puts your drive shaft where it needs to be. Lift a truck the shaft pulls out, lower one it pushes in. This mod will help you too. This is why my blocks are true custom blocks for made for particular drops.

Alright I'll see what I can do. Thanks, I really appreciate the info.

also, I forgot to mention, since you already have 3" blocks you can just use your ubolts you have now, I also offer blocks sold separately. About $62 + shipping.

A free mod you can try is to go underneath and spin your carrier bearing 180 degrees. It's as easy as removing the 2 bolts, spinning the bearing on the drive shaft by hand, then re installing the bolts. This should raise the middle of the shaft about 1/2" and may kill that vibe. My blocks can be seen by clicking my signature here on TM, which takes you to the streetacos.com website, then search blocks. High quality kits with or without low profile bump stops. U-bolts are custom made for me by a spring shop I use and quality is far superior to others commonly seen. Thanks for the contact!