Basic steering 101, which I'm just putting out there cuz some people don't know but I'm sure you do. Make sure your tires are the right pressure, make sure you get all of the joints greased. Even the idler arm. It's a giant pain in the butt.
Have you put the front end up on jacks and then pushed the wheels back and forth by hand? It does take some effort but if you can put your hands on the 9:00 and 3:00 positions of each wheel, you should be able to turn them back and forth to the stops.
Is there any way to reliably reproduce the situation?
When you have to Armstrong it, can you hear the power steering pump whining?
If none of the linkage is binding then you probably lost a bearing in the steering gearbox, and would be right to replace it.
Ever run over anything, or clip an animal? Does it always happen at low speed? Accelerating decelerating? If you did manage to bend something and it's only binding when you're on the brakes turning left that could be it too.