1998 Dodge 3500

Short history: Hydroboost brake booster was leaking power steering fluid so I took the truck in to have the booster replaced. Now after the truck has been driven about five to six miles the brake pedal feels like it is catching when I first apply the brakes. I have to push harder and harder to get beyond the catch to apply the brakes and when the brakes start working they will shake the truck as the brakes are stopping the truck in an aggressive manner.

The shop has installed a second new booster and the truck is still having this problem.

Anyone have an opinion as to what is causing this problem?