Speedo Calibration Issue

latest revision I've installed is 9r31, adjusted parameters too axle ratio 4:88 and tire size 33"
when my speedo is reading 60mph, gps shows me doing 46mph, so 14mph difference and it trips the service trailer brake and abs light within half a mile of takin off.
2008 Silverado 2500HD 6.0L gas with 4:88 gear and 33" tires for winter lol

[mikel]

how far off is the speedo with no changes made?

With stock tune when the speedo reads 60mph the gps reads 52. So 8mph.

So I've re-installed the diablo tune. Put in axle ratio 4:88 and set the tire size to 25.5" and the speedo is bang on and the service trailer brake and abs light have cleared.

Good job. Learn somethin new every day

ok So I'm back on here with same problem as I original had except now I have installed my 37'" tires and the service trailer brake keeps tripping and abs I have tried all the previous steps that worked last time. but not as lucky this time so back to the drawing board