I tried to lower the rear of the truck to level it by using shackles on the rear leaf springs. I then noticed a slight vibration that would not go away.Put it back original,no problem, vibration gone. Apparently it was something to do with the angle of the drive shaft causing the problem.Gmc has the rear of these trucks jacked up 3 or 4 inches,probably for load hauling which I don't do. How else can I get the rear down without a lot of hassle. Not much into lowering kits and so forth.Thanks in advance for the input.

 

Wow thats weird I have lowered trucks that way for years and never had an issue. Anyway you drop it is going to change the angle. 2 inches should not give you a problem. Not to doubt your ability, but are you sure they were installed correctly. If you install some of them backwards the leaf spring can come in contact with the center section of the shackle. This might give you strange feeling/vibration especially on bumpy roads.

 

I never got any vibration on mine and I dropped only the rear 5 inches. I also put new U-Joints on my shaft too. Then I put some plates to compress all the leafs to reduce axle wrap. That helped a lot.