[hatzie]

As I stated in my prior post. Hydroboost isn't some scary different extra part. It serves the same function as the vacuum canister booster on smaller gasoline trucks. Hydroboost is used on 30-60 series and diesels because the assist is instant. The big 1 ton and larger truck brakes need more assistance and Diesels have no manifold vacuum and a much heavier engine over the front wheels.
A failed assist, either vacuum can or hydro boost will make the pedal so stiff you will almost not be able to push it down. Just like pushing the brake pedal with the engine off and the vacuum line off the vacuum booster.

A failed booster will not give you a loose pedal that pushes easily all the way to the floor. Pedal to the floor is ALWAYS in the brake side of the system not on the assist side.

You have one of the following three or a combo... a leak in the steel or flexible brake fluid lines, leaky wheel cylinders, or a failed master cylinder.

Throwing expensive parts at it will empty your wallet and not fix what's broken.