I have a 1995 Ford Escort LX Sedan that is having mechanical issues, but not sure where to start with diagnosing the problem. When driving the car, it bucks driving down the road, doesn't downshift going up a hill, and when in overdrive it still bucks when not in gear. I replaced the Throttle Positioning Sensor, and the bucking still continues. What could be causing the issue and how could I go about fixing it?