when I start my truck in the morning and let it warm up then when I go to leave and I touch the breaks they lock up on me, but when I take my foot off the breaks it will release and if I push them again they lock up again! It will do that about 4 or 5 times then it stopes! If I let my truck sit for the rest of the day then go to leave it will start doing it again! What could be the problem? Thanks,