1993 Dodge Shadow Throttle or Speedometer Sensor

I have a 93 Dodge Shadow that was running in perfect conditions. All of a sudden it will take some time to shift into the next gears. It will up to 30-35 Mph then the gear will kick in instead of shifting at 25 or below. Now the car won't advanced either forward nor backwards. I've already changed the Transmission Filter and nothing happen. I've been reading and searching in the internet and found that it could be the Throttle or the Speedometer Sensor. Which on is it? or is the Transmission solenoid that I have to change. Please advise.