When this happens, does everything that operates only with the ignition on FAIL? Things like:
Allison shift pad light goes out
Dash HVAC fan quits
If so, next time this happens, check voltage IN and OUT of the IGNITION SOLENOID. The ignition switch signal closes the contacts in the ignition solenoid to then supply all those things that operate with the ignition on.
You could also hook up a test light or voltmeter to the OUT of the ignition solenoid to get a quick readout on what is happening there.
If power on the OUT side of the ignition solenoid fails, it could be one of three things:
Bad ignition solenoid
Bad ignition switch (signal not getting to the ignition solenoid)
Wiring problem between the two.
An ignition solenoid failure will not leave you stranded. You just move the cable from one large lug on the solenoid to the other. Then to turn off the ignition, you would just remove it and return it to its original lug.
Ex: 2003 Alpine 38FDDS. Ex: 1997 Safari Sahara. Ex: 1993 Foretravel U240