Next time on the autobahn use the digital speedo:

realtime MPH, tach, etc...on your odometer.
do the Odometer test

Hold the Odometer button in, turn the key to "on" position.
continue holding the odometer for about 5 seconds, it will flash "test" Let go of the odometer button.

Everytime you push the odometer button it will do a differnt test, Gauge sweep, MPH, etc... one of them that says "tac" will be your Tachometer in real time digital.

when you see "tac" on the odometer, start the truck and see where it idles in real time digital.

There is real time MPH, gauge sweep, lights all dash lights, Battey voltage, real time tach,