Front end alignment

[pontiacvince]

I've had my Suburban aligned at 2 different shops. The first had no clue how to align a '71 Chevy Suburban with 2" lowering springs and a quicker ratio steering box. They had attempts to get it right. It just plowed when turned all the way in either direction, and at highway speed wanted to wander all over the place. The second shop got it much closer (after 2 attempts). It still feels twitchy on the highway. All other suspension is new and stock replacement. I never had such a hard time getting a vehicle aligned properly in my life, and it's not like it's some exotic foreign POS. It's a FU%^ING Chevy!!!
Any suggestions appreciated.