Its started when my brake light and antilock brakes light came on after i put bigger tires on my truck....305s!!! I noticed the lights turning on and off sometimes after a few minutes sometimes after i hit a major bump on the road somtimes not at all...i took it in to a dealer to get a diagnostic check and several codes came back to the ABS module...I got a junk yard product that was in good condition because brand new the part would run me $1,500 my baby is worth it but lets face it money like that is not easy to come by...so I got this used part and I had it installed and the brakes were bleed. The boys at the dealer did another diagnostic check and the codes never came back...but i realized when I drove off the lot my brake pedal was not as hard when i would press down on it as before it went into the dealer. My mechanic recommended me changing out the master cylinder and I did that and I took the air out of the brakes and still the brake does not brake properly and i am out of options. Anybody have any suggestions or a path to guide me towards it would be a big help...thanks