GPS vs. Radar Gun

I have a GPS that has a feature where it displays my max speed. Can I use this as evidence in traffic court to get out of a ticket?

It is very unlikely that this would hold up in court. Most GPS units only have an accuracy of 3-7 meters at best. This can also be reduced by cloud cover or tree cover. The accuracy of the speed is also affected by clouds, trees, and tall buildings.

Police Radar Guns such as the Decatur Speedtrack are carefully calibrated at the factory and are supplied with tuning forks to verify their accuracy. They are certified for law enforcement use, and by law, they are checked regularly for their accuracy. While you are more than welcome to try this, I would highly doubt that a court would take a GPS reading over a Police Radargun.