I've been going crazy trying to figure out why my rear-end is shuddering (bad) lately, and was hoping you all could help me.
I apologize up-front for the length of the post, but wanted to give you as much info as possible:

Background:
Action: Bought new truck ('99 SC Flairside Lariat)
Result: Rides good, very smooth
Action: At 13k miles, installed pre-01 Lightning wheels with 285/55 18 Pirelli Scorps
Result: Bumpy ride
Action: Checked tire pressure - 40psi, reduced to 33psi all around
Result: Somewhat better, still not like stock
Action: Replaced stock shocks with Edelbrock IAS shocks on all corners
Result: Smooth ride, as good as stock
Action: Tire rotation and balance at 18k
Result: Bumpy ride returns shortly after rotation and balance
Action: Checked tire pressure - 40psi, reduced to 33 psi all around
Result: Little better, still way harsher than before rotation and balance
Action: Returned for a re-balance, found one wheel off 1/2 ounce and 2 wheels off 1/4 ounce - adjustments made
Result: Little better, but still "bouncy" and harsh ride
Action: Installed Hellwig traction control springs (helper springs)
Result: No noticeable ride difference
Action: Installed Hellwig rear anti-sway bar
Result: Ride even harsher, but corners well
Action: Removed Hellwig traction control springs
Result: Ride a little better, not as harsh, but shuddering at highway speeds, and bumps are not taken as well as they had been
Action: ???????

Current Mileage - 19.5k
Truck Age - 3yrs 2mos
Miles on Tires/Shocks - 7k

Any suggestion on what to check and/or replace would be appreciated - my truck used to ride so well after the wheel/tire/shock upgrade, and now I don't enjoy driving as much because I'm shuddering and shaking teeth out.

Thanks,
SlickWilly

 

Have you tried rotating the tires? Might just be one bad tire....also could a weight have come off causing it to be unbalanced again?
Also another thing it could be but I doubt is bad bearings.

 

Find a buddy with stock wheels and tires and swap for an hour. That should help you narrow it down a lot.

Possibly it could be your driveshaft out of balance or a bad u-joint. Maybe a bent axle.

Your truck is pretty low miles - I am suspicious of the wheels/tires.