RepairPal Certified shops can diagnose and repair your 2008 Pontiac G6. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.
Just don’t drive at that certain speed!
A professional scan test during test drive will determine if this is an output signal failure OR it is within the speedometer itself.
The ‘source’ of the failure must be located before it can be repaired - *hands-on* testing will provide the location. Good luck!