Steering Mystery - I Need Help!

[truckster]

I have a 1972 K/5 Blazer 4WD with factory power steering.

The front U-joints were making noise, so I decided to replace them. As long as I was going that far, I decided to replace everything under there, from the carrier bearings out. I installed new upper and lower ball joints, tie rod ends, new spindle and wheel bearings; everything replaceable. I used Spicer, Timken, and Moog parts - no cheap stuff. I also installed 3 degree caster shims between the leaf springs and the axle perch with the fat end toward the front. I set the toe-in at 3/16".

I just took it out for a drive and it's all over the road - way worse than before. Everything is tight when it's sitting, but I get up to 25 MPH and I have to make constant corrections to stay in my lane. I've thought about pulling out the caster shims, but maybe I'm missing something.

Any ideas?