Speedo WAY off....

2001 Sebring LX, Tires 205/65-15, I just purchased this car and noticed the speedo is off. I drove the car on the highway with a gps and realized a difference of about 20kph. Speedo was reading 130kph, gps registered 109. I tried this in a wide range of speeds and it's off pretty bad. I originally thought it was the tire size but ruled that out quick enough. I'm unsure if there was any tranny work to this car, so my info is limited.

Any thoughts would be appreciated.