4x4 steering issue - won't return to center

[GMC-YA68]

Guys, I am in need of some help and this section gets a lot more attention.

I originally made a thread in the blazer forum about an issue with my steering. Long story short, after I completed my swap my steering will not correct itself back to center after turning. It turns and stays turned which makes it very sketchy to drive.

New 2.5 lift (all spring) with extended pitman arm (additional drop)
New poly body mounts / transmission / transfer case mounts
New tie rod ends / drag link ends / drop pitman arm. drag link is perfectly even.
New wheel bearings / new upper and lower ball joints. The spindles move freely and are not stuck by any means.
New intermediate shaft. New U-joint and rag joint.
Hydroboost set up using the flow control valve from factory power steering pump.
Alignment is good.
I've had both a brand new 18:1 and 15:1 box on it.
Caster is good (positive caster)
Camber is level.
I've got some 18x9 wheels on it with 4.53 back spacing and brand new Toyo AT 325/60/18s.

Here is the other thread I started but haven't found a fix yet. I have not tried a different set of wheels since she has been back together. My original wheels were rusted with dry rotted tires so I don't have them any more.
http://67-72chevytrucks.com/vboard/s...d.php?t=688321