Digital speed source same as speedo?

[Cupton]

Curious about something. Is the digital speed in the DIC getting its speed from GPS or from the truck itself just like the needle on the speedo gauge?

 

2018 Sierra SLT, All Terrain. 
 

Thanks! 
 

[CamGTP]

Same place as the needle. It's all done over CAN-BUS.

 

The needle can just lag behind slightly because it's still using a stepper motor to move it.

[jrmcswain]

I know when I got my truck back from Hennessey, I had a custom driveshaft made so I could raise the speed lim AND iter because I'd top out before the end of the 1/4 mile. I had to set the top speed AND switch the source in the programming. This was something new starting with the 2017 model year.

[Cupton]

Thanks guys! The needle does seem to be 1-2 mph off (slower) which is what prompted me to ask.