Steering puzzle

[72K10]

My 72 K10's steering will pull to the right, then jerk back to the left when I turn pull hard enough. It will begin to pull right, then I'll start to turn the wheel left, and it will get harder, then it will sort of pop free. Sometimes it will "catch" harder, and I'll have to really lean into the steering to get it to go left. Nearly always there is sort of a "pop free" feel, like something was catching, but then with enough force to the left, pops free.

That ain't the hard part. The puzzle comes in because I've replaced every component of the steering I can think of. Both tie rod ends, drag link front and back, pitman arm, steering gear, power steering pump, hoses.

The feel when it pops over is like it was riding on a ridge to the right, then comes off it when I turn left, but it gets hard to turn left.

I thought it might be my tires, so I switched right front with left front. No help. Then I switched rears with front. Same symptoms.

What could it be?