2004 Columbia (no power no speedo)

Have a 2004 Freightliner Columbia, CL12064S, with a Detroit series 60, and a Fuller 10 speed. Several times recently, while driving with a full load, on flat ground, the speedometer will suddenly quite working and the truck will loose power. It acts like it is in a "power down" safety mode of somekind, allowing the vehicle to travel at limited power (20 mph). There are no warning lights on the dash, and the oil pressure, engine temperature and voltage are in normal ranges.
If you shut it down and restart it everything seems to work fine. No need to wait for any period of time before restarting either.
There are no Diagnostic Trouble Codes in the system, in history or active.
Any thoughts?

 

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Wouldn't that cause a Diagnostic Trouble Code that would be able to be seen as either ACTIVE or INACTIVE. We are getting zero codes. None.
???????