I have a 2004 5.4 Triton FX4 OFF Road. The other day as I put the truck in reverse after about 5 or so feet it seems the rear passenger side wheel locks up. When I jack the back end up and put the truck in reverse the wheels spin forward and reverse fine. So I have ruled out that its not the back brakes locking up. It seems like when the weight of the truck is on the ground thats when it locks up in reverse. does the speed sensor control the gears on the inside of the rear axle? If so maybe the speed sensor is bad and preventing me from going into reverse?