1998 Dodge Durango

My abs and brake lights both recently came on, 2 days after my brakes were visually inspected by a trusted mechanic (a cousin who happens to be a mechanic). I have no speedometer until I hit 40 km/h, once it's there, it works perfectly. The same is true on deceleration. You go from 60 to 50 to 40 to 0. The problem exists whether it's in d, 2, or 1. And it doesn't change if you turn the overdrive off. Any suggestions?