Ok guys, heres a good one:
My truck, with on 83k on it, never has been off road or towed anything heavy. I have developed a vibration/shutter while excellorating or under heavy load. Dealer says I need to spend $3000 to replace rear axle, differencial gears. Local mechanic said it was only u join. Went with U-joint for $300. Sounded like a better deal. We now the vibration is gone during excelleration, but reappears at about 50 mph and stays there until I drop down under 40. Dealer said they had it up on lift, and left wheel was not spinning as fast as rear. They never took it apart, so now could they know it was the axle spline. Anyway, I thought that with a limited slip diff, one wheel would not spin when up on lift anyway.
Please help guys before I trade this thing in!!! 
More info on truck:
2002 4x4, with electronic locking rear diff
One more thing, it has always had what the dealer called “axle rap” since new. They said it was “working normally”. Also have recently noticed a clunking when shifting into gears in driveway.
With an electric locker, it will behave like it is open when unlocked.