What PSI are you running your shocks at? I have the same lift and 35" tires and I don't remember feeling what you described. My handling improved after I upgraded my suspension. My tires don't like it be I do.

 

Are the tires to wide for the stock rims? If so, pinching a larger tire like that will give it a smaller contact patch. Just a thought.

 

I have a 2" Thuren Suspension setup on my 2007 QC Longbed. I also just upgraded to 35"x12.5x17 Toyo MTs and have the same feeling like the back end is tracking different and is squirly. I first had BFG 315 ATs when I got the new suspension and didn't notice this at all. So therefore, I think it's the tires. The tall tread on the Toyo's is very flexible and I think that's what's causing it. As they wear down it should get better. It does make the truck less highway friendly but I think I'm getting used to it. I'm running approx. 50 psi front and rear. These tires do hook up well, much harder to spin them than the 315 BFG At's.

Sounds like we're in the same boat. I might go with a less aggressive tire next time.

 

Try some XAT's...they stay VERY planted on pavement.