The speedometer not working would definitely result in the transmission shifting hard and/or erratic.
Since you noticed this problem after the service job, it could be caused by the oil change or emission test if wiring connectors or connections were worked on.
It could also be coincidence that the sensor decided to quit at this very moment and the only way to find out is to go back to the service person who handled this job to have a check.
Costing would depend on what comes out of the diagnostics.
Let us know how it goes.
Wednesday, November 13th, 2019 AT 5:58 PM