Google: Ford Ranger Instrument Cluster Self-Diagnostic Mode
See if there are any "codes" that come up, this is also called Instrument Cluster Engineering Mode
The newer dashboards use a built-in microprocessor so "second computer", it does "talk" with the PCM(main computer), but this micro-processor controls all the gauges on it's own, as you will see in the Test mode.
What you described is what happens when engine is off, truck is stopped(assuming no speedo MPH) and key is On, all the gauges showed low(0) and all the lights associated with key on, engine off, came on.
But engine remained running, and running fine from your description, so I would think PCM is fine, but micro-processor should be looked at.
Last edited by RonD; 03-17-2016 at 07:16 PM.