So here is my Issue.

I got larger tires on my Truck not too long ago.

I did something (reset distance study i think) to correct the speed on the digital speedometer.

Last week, I user a Tuner to correct my factory speedometer to account for the larger wheels.

I reset the distance study again, but the z2 seems to still be showing the speed with the factory tires while the actual truck speedometer shows the correct speed.

Any ideas? Do I need to reset the unit a different way?

go to settings, hardware, 3d calibration, and reset the calibration, so that it can recalculate based on the larger tires. I have larger tires, and mine reads perfect now.