No speedometer is the clue. One of your wheel speed sensors is probably bad. Any work done down around the wheel hubs lately? If the fault comes back immediately when the truck is started after being reset the speed sensor is open circuited or shorted, if it takes a while (less than probably 100 yards) it either the tone ring is cracked or full of rust, or the sensor head clearance is to big (if you removed and reinstalled it).