Speedometer

Dodge neon, 1995, 122,000 miles manual transmission
i recently purchased a used neon sport and about 2 weeks ago started having problems with the speedometer. Prior to this I had to replace the clutch and transmission. After the transmission was replaced the problem with the speedometer started. What happens is while driving the speedometer will start to bounce and when it does that the car seems to feel like it will lose power. It kind of jerks. It mostly does it while on the freeway. It does it a little bit driving in the city but always on the freeway. Is there some sort of fuse or sensor that will cause the speedometer to do this and the car to jerk? If so how can I fix it? Also the speedometer will sometimes register zero and the mileage will not work either. Help!