Check your steering components. Have somebody turn the wheel sharply 30° back and forth while you crawl around underneath and put your hand on each and every joint. Drag link ends, tie rod ends, rag joint, box to frame mount and then pick the front end up. Push/pull on the top of each front tire while somebody looks at both upper and lower ball joints for play. There should be none. Use a pry bar under the tire to see if the ball joints have any slop up and down.
If you feel any slop in the steering joints, replace the parts.
If all this checks out ok or you replaces stuff, get it aligned and the problem still happens.
Pull the power steering belt and take it for a drive. That will eliminate hydraulic influences on the steering.
While you may find your hydroboost is faulty, it has no direct relation ship to steering other than fluid flow. That means a bad booster is just a bit worse than your steering box. With brakes, a bad booster just means you have to push harder. It has nothing to do with side to side braking.
You did put on new parts, not other used ones?