First try adjusting the back brakes, you can do this by going in reverse and braking many times. The best way is to do it manually, behind wheel theres a little slot, were you can adjust them if you have a screwdriver. If its not the adjustment, then i would check your master cylinder, its not uncommon for them to go out, and if they are out, you will notice the peddel squash to the ground when trying to brake. i just ordered a upgrade kit for my truck, but ill tell ya once you adjust the brakes, it makes a huge difference. i couldnt stop my truck worth crap when they wern't adjusted. Ill post a review of my kit once i get it installed and tested.