I have what would be considered a high mileage GT and have had absolutely no issues with the car since I purchased it in '06. On Saturday I drove the car to a local warbird show and had the speedo stick at 40mph. It will fluctuate about 2mph at speed and stays at 40 when the car is off. When I got home I disconnected the ground for about 30 min to see if the system needed to reset but nothing changed. Drove the car today (approx. 80mi.) with no change. The battery is original, works great and has been maintained with a 'Battery Tender' float charger. Has anyone had a simular issue? Where should I start? Thanks in advance, Tony :usa