i took my truck to autozone, the code told me it was my gas cap, i replaced the gas cap. a few days later reverse went out, then my 3rd and 2nd gears went out. So i replaced the transmission. it still wasnt shifting and the speedometer wasnt working, so we got a dierent transmission and the same problem occurs. So i am stuck as to what is wrong with my truck. With replacing 2 different transmissions and the speed sensor, what is the problem?