Around 65 my ABS light comes on and then intermittenly thereafter, my parking brake light will flash, though it wont engage. Also, the vehicle wont upshift until it revs to a high rpm. Could this be an actual mechanical problem, or a faulty computer sensor?

 

Crawl under the truck and inspect the wiring going to the rear speed sensor in the top of the differential. I've seen a few trucks where the wiring gets chafed and broken near the sensor, usually when hauling/towing something heavy or on lowered trucks.

 

Defiantly the first place to start. I've had to repair that wiring so many times, but because of the gravel roads the vehicles traveled on, just destroyed the wiring and connector. There were a few times I had to replace the sensor as well. Good call Quintin.

 

appreciate the info, i will check it out this evening.