Brake issues

I've got an 03 Tacoma SR5. When i apply the brakes everything works fine until right before the truck comes to a complete stop. It then acts as if the brakes lock down. Sometimes, after I stop, I can let go of the brakes & the truck sits still. If I tap the gas & the truck lunges forward but comes to a stop again without pressing the brake. Once I give it enough gas the brake releases & its back to normal operation. I've taken it to the mechanic twice but theu have not found anything. Only problem is it only does this about twice a week. Sometimes it shakes the truck violently as if i am slamming on & off the brakes as I come to a complete stop. Has anybody else had this issue? The mech wants me to leave it with him for a week so maybe he can catch it, but I dont want to be without my taco for a week. Any help would be great. Thanks in advance