2005 GMC C1500 BRAKE PULSING

I RECENTLY HAD MY FRONT AND REAR BRAKES DONE ON MY TRUCK. I REPLACED THE FRONT ONES MY SELF BUT HAD THE REAR DRUMS DONE AT A SHOP. MY FRONT ROTORS LOOKED CLEAN AND EVEN SO I DIDNT HAVE THEM TURNED. THE PAD WERE PURCHASED AT PEP BOYS. THE MOST EXPENSIVE ONES THEY HAD. I USED A C-CLAMP TO DEPRESS THE CYLINDERS TO PUT THE PADS ON. NOT BLEEDING THE LIKES. I'VE DONE THIS IN THE PAST WITH OTHER CARS AND HAVE HAD NO PROBLEMS. AFTER DRIVING IT FOR A FEW DAYS, I STARTED GETTING A PULSING BACK THREW THE PEDDLE AND A VIBRATION WHEN I PUT ON THE BRAKES LIGHTLY. WHEN I PRESS IT HARD IT USUALLY GOES AWAY. THE FASTER I GO THE FASTER IT PULSES. I THOUGHT I WARPED THE ROTORS SO I TOOK IT TO THE MECHANIC TO HAVE HIM CHECK IT OUT. HE SAID THE PRAKE PADS WERE CHEEP AND I WARPED THE ROTORS. SO HE REPLACED THE PADS AND TURNED THE ROTORS. IT SEEMED TO BE GONE BUT CAME BACE GRADUALLY. I JUST LEFT THE SHOP WHERE HE TURNED THE ROTORS AGAIN, BUT IT IS STILL DOING IT. DID I WARP THE ROTORS, OR DID I POSSIBLY MESS UP THE ANTILOCK SYSTEM? PLEASE HELP. THANK YOU.