I was towing a 3 horse gooseneck trailer everything was fine. I was backing into a steeper driveway when out of no where I couldn’t go backwards anymore. Tried to go forward nothing. Brake pedal started going up and down on its own and when my foot was off the brake the trailer brake controller stayed lite up with numbers on it. All brake were just locked up. First I unhooked the trailer 7 way no change tried fwd and rev again no go. Pulled the ABS pump fuse things let go then tried to go and things locked up again. The only time that brakes would let go is when the truck is in N and I shut the truck off. The more the RPMs the harder the brakes will grap. I’m thinking the hydro boost or master cylinder. I am leaning more to the HB because my PS sometimes feels like it’s not working when first takeing off and turning at the same time. Has anyone ever delt with this. If not the HB or MC what could it be.