ever since i did the brake pads/rotors on my 2002 silverado 1/2 ton i have constantly had problems stopping. the rotors are the exact same specs as stock but slotted and i have hawk pads. at first they were really bad and a local garage told me to add a proportioning valve to the rear brakes to boost the pedal pressure...did jack shit. then the rotors were glazed with 1000 miles on them so i had them turned down and bought new pads because i wanted to be sure it was right and the pads were glazed too. then i did stainless steel brake lines...helped with stopping but pedal pressure and height still sucked. and i was just under my truck and next to the transfer case, and torsion bar on the drivers side attached to the frame there is a black box with brake lines going into it, and it has 2 plugs one big one and one small i unplugged both of them and took it for a ride and thought my head was going to go through the windshield they worked soo good and the pedal was nice and firm. and i obv know i cant leave it like that i was just troubleshooting but what could cause the brakes to be shitty with it plugged in? is it a sensor that isnt doing its job correctly? what can i do...?