1999 Bravada Brake Pedal Pulsing

About 2 years ago I replace the wheel hubs myself. Recently I had someone replace the ball joints. Afterwards the brake pedal was pulsing, similar to when the ABS is trying to keep the brakes from locking up. No ABS light came on. The place that fixed the ball joints said they had nothing to do with the brakes now working improperly. I took it to get a second opinion at a brake repair shop. They assured me it was the brake power booster. After replacing the master cylinder and power booster it still has the pulsing/grabbing when you brake. They are very adiment about bringing it back so they can figure out and fix the problem for free. (I am now assuming because they misdiagnosed the power booster problem) Anyone have any ideas. All I know is my brakes worked fine

Welcome to AF.
Has this been going on for 2 years?
As to your repair shops fixing the problem that is between them and you.
We are staying out of that.
But my advise is.
If they said booster would fix it and put it in writing I would take it right back and ask them to fix it on there dime.
If it is a ABS brake problem you need to get it on a ABS capable scanner and get the code when it is acting up.
And check for codes before you turn the key off.
Post back your code no.