Sounds like you need to reduce your tire size to bring the Gryphon's speed down to match the GPS's speed (if you trust your GPS). Once you get the Gryphon speed accurate, the dash speedo will just be whatever it is.
You could also base this on distance. Longshot270 posted this approach: Drive 10 miles on your GPS. Divide that by what your trip odometer says. Multiply that result by the current TS you have been entering. The resulting TS should be very close to what you need. If you drive farther, say 20 or 50 miles, your results should be even better.
- Jack
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