Driving down the road today, and the speedometer was at 45 then it just started jumping around then the ABS light came on and then it started to down shift and rev up and up shift. It shifted really hard when it did. I shut it off for about 20 min but it made no difference. Its a 4x4 with the 5.4. whats wrong? is the computer fried or what?
It sounds like the speed sensor that's mounted on the top of your rear differential is either malfunctioning or there is a problem with the wiring. Both your speedometer and your ABS use this sensor to operate, and so this is likely your culprit. I would check over the wiring and sensor and replace as necessary.