91 GP Speed Sensor question

I need to know if anyone can help me with this probem. My speedometer and odometer is off. I have the correct tires, P205-70R15 on. It seems that for every 10 miles the odometer is off by 2 miles. My speedometer is apparently off too. I just got a ticket for speeding even though the speedometer didn't show I was speeding. I pulled the speed sensor out and cleaned the dirt build up from around the magnet. I also changed the fluid and filter before my ticket, so I know its wasn't that.
Is there anything else I could check or is the speed sensor bad. Any input would help. I have a 4 speed auto RPO ME9.

Thanks

Found problem. Seems the previous owner replace transmission and switch the pickup inside the vehicle speed sensor housing. The pickup had 11 teeth instead of 14 teeth that I needed. A quick trip to the salvage yard resolved the problem. Speedometer and odometer right on the money.