I had a vibration around 50-60 mph, thought tires until I rebalanced them myself. I also started hearing a clicking sound at low speeds. After checking my front diff ring for lost teeth I wrapped a tow strap around the front driveline and pulled to correlate the clicking noise to the same spot on the driveline, ie not the pinion bearing as that would move with each revolution. Couldn't feel ANY slop in u joints but it was either that or pinion gear. U joints were cheapest option too at <$9 per joint. Lifetime warrantee were $15 each but not able to be greased as they have synthetic grease, I have a grease gun with amsoil synthetic marine grease already so the cheaper ones will be full of synthetic grease anyway.. Pliers to remove the clips and a large socket and a smaller one and a machinist hammer was all it took. I did remove the driveline from the truck as it's easier to do that way. I also cleaned out the slip joint and greased that with synthetic grease while it was apart. Ended up that only one of the eight u joint bearing cups were bone dry. All the others were greasy! That was causing the vibration and clicking I was having!! Btw the joint had no slop to it like every other bad u joint I've replaced..
2006 Nismo KC 4x4 6speed
Volant CAI with the PowerCore filter and ram air part (modified because VOLANT Q&A SUCKS and parts wouldn't fit)
Axle vent with a 90 degree elbow (axle was threaded with 1/8" BSPT threads according to hydraulic shop I went to.. go figure)
Oh yea fixed the lame cargo light always coming on with door open mod thing.
Swapped rear diff with amsoil
Swapped front diff with amsoil
Swapped transfer case with amsoil
Swapped 6 speed manual trans with Redline mt85
Added some LED fogs to blind the idiots with drop in hid kits