Gene; Thanks for adding info to your signature line.
As Richard says the 12v power on the dash lighter socket would not be connected to the same fuses as the ECM, ( Engine Control Module ).
Your lack of throttle response , could be signs of a lift pump failure or problems with the TPS, ( Throttle Position Sensor ) under the pedal on our vintage of chassis.
Freightliner/Cummins uses 5 fused battery feeds to the ECM as well a ignition power, the 5 battery fuses are in a module in the engine bay, that from the factory had a plastic shield surrounding it. Over the years that plastic can fall apart, leaving the module exposed to water being sprayed through the engine bay on wet roads. So there is the possibility of corroded connections at those fuses, one of those fuses is for the lift pump power feed, that the ECM turns on once it sees ignition power.
5"x5" box in the picture below, the boxes may be in a slightly different location on your coach; but location is limited by the length of wiring.
There are several posts ongoing about , hidden locations of secondary fuel filters, something to consider too. But I don't thing a plugged secondary filter problem would be as erratic as you describe.
I'd say time for a lift pump pressure/flow test and checking the TPS with a scan tool. You could check the wiring connection, from the TPS to the dash harness under the dash, humidity from carpet cleaning can cause issues there.
Pictures show the fuse set up for my Cat , your Cummins will have more fuses in this location.
Parts of the plastic cover visible, where the module attaches to the firewall.