Hyundai Repair: Elantra trans speed sensor, timing belt replacement, speed sensor

Question
Dealer diagnosed trans problem (hard shifting, safe mode, etc.) as needing speed sensor.  Don't know if input or output sensor.  Is this difficult to switch?  Is the part attached externally?  Also, would you recommend dealer for timing belt replacement?

Answer
Yes dealer is the best way to go this is hard thing to do being the belt need to have tension on it for atleast 1 hr before setting it to the right adjustment so that it dont jump after the job is done,with out the code i cant say whats wrong so sorry