In my 99 Laramie SLT overhead console everything works, except for the trip meter. I ran the self test on it, and it said "PASSED". My friend's 02 Laramie SLT does the same exact thing. We don't get any errors on the display either. Anybody know why this is happening? It's not a big deal as the dash has its trip meter, but it's just an annoyance that it doesn't work.

Mine is the exact same...

Is it possible that it was an option for overhead console, but never got linked to anything that gives it its information

The only thing I can say is to verify the CCD network is plugged into the overhead module. Without the CCD network the overhead computer can get any data from ABS, PCM or the ECM. ABS controls the speed and distance. The PCM sends the fuel level signal and the ECM sends the fuel consumption rate. The sad part is the MPG part is typically way off the mark because it only calibrated for stock injectors and no tuner.