I have a 6 inch BDS lift with bilstein rear shocks and on the express way when I'm cruising at 70 the rear end bounces real bad consistently, when I get on it it'll smooth out though. Why could be causing this?

 

A lift will do that

 

Slipping differential. The clutch packs could be bad, or replace the fluid and put friction additive

 

The diff has nothing to do with it. Your rear is higher so its less stable, when you accelerate you add more torque which plants the rear tires resulting in better traction and more stability. Tire also play a big part in this, if your tires are worn they wont grab the road as well.

 

There brand new mud grapplers so I'm guessing its just the rear end being light in weight and higher up

 

Yeah it's the lift my truck does it

 

I've got a 6 inch rcx lift and 35" trail grapplers and I do not have this issue. Also I would think that any rough ride from tire ***** would be less noticeable at high speeds I only feel any at just a slight roll

 

I would think a rear end balancing would help. If it goes away when you speed up I'm thinking tires out of balance. i could be wrong.