I'd go ahead and change the fuel filters. If you can get the primary filter cut opened, it might reveal algae bloom. If so, then get Power Services product and spike the tank to kill off the algae. (Or, see if a mobile fuel polisher might be available to clean the tanks fuel.).
Suggest if not running the coach and engine to temperature, that periodic starting/idling or even fast idling - is really not helping (And could be hurting.) the engine more then it's helping...
I do also recall reading of a fuel problem being tracked down by a mobile tech doing a temporary install of a pressure gauge between the fuel line and the Lift Pump - that could show if you have a fuel supply problem to the Lift Pump. If so, back up, and have the tech move that gauge to in front of the Primary Filter, and see if you're having a Tank Fuel Pickup Problem.
I'll follow the thread to see what other's suggest, and also as you work our way to a solution...
Best of luck,
07 Country Coach Magna Rembrandt 45' ISX600
Roo II was our 04 Country Coach Allure 40'
OnDRoad for The JRNY! Enjoy life...