I35 Speedometer Error Update

[shortimer]

Greetings,
Back in January I posted a message about the speedometer reading being different when compared to the trip computer's reading of the speed. It was 3-4 miles under what the dash speedometer showed.
Since that posting I bought a Garmin Street Pilot III GPS system. On a recent 200 mile trip I checked the GPS reading against the dash speedometer and found the GPS reported my speed to be 2-3 miles per hours slower than the dash reading. I still have not got hold a nice laser radar gun to do an accurate test but I'm pretty sure my dash gauge is off. I just don't know why. My car does have the "sport package" which gives me slightly bigger tires. No clue if that has anything to do with things. I would hope Infiniti has the transmission programmed correctly for a sports package option. If I find out why there is an error I'll send another post.
Regards,
Shortimer
2002 I35
P.S. I got to drive a 2002 Q45 last week. That's a nice car!