shudder after spring install

[n54power]

I replaced my lift blocks with a procomp full leaf pack. From what I figured out about my lift is that it was a skyjacker. The procomp leafs are for their 6.5" lift kit. Is it possible the extra lift created a shudder?it's only at about 15mph to 25-30MPH.
I was thinking replacing the skyjacker spacer with a procomp one.

 

[tbsimmons]

If it changed the pinion angle. Does it shimmy no matter the throttle input?

 

[n54power]

It only shimmy at the posted speed. Before the spring pack I was sitting about 1/2" low in the rear.now I'm roughly 1.25" high in the rear.
The shim was for a skyjacker 6" lift. I installed procomp springs that are used in their 6.5" lift kit