Im not sure but i would check your brake fluid resevoir then take off your wheels and look for any leaking brake fluid or a pinched brake line. I had the same problem because when I lowered mine, I accidently dropped the spindle and it bent the brake line up causing brake fluid to leak everytime I hit them, I loosened it and then pounded it down with a hammer. I put some more brake fluid in the resevoir and hadn't had problems with it.
What year is your taco? MAYBE could be your master cylinder but very unlikely! Hope it helps! If all else fails, a good mechanic can hook you up!