Have you unplugged from the campsite and found that your power plug was pretty hot? Perhaps you are tripping the 30 amp breakers pretty often.   Or, like some unfortunate D owners, you have actually seen smoke and smelled burned rubber as your power plug got VERY hot.
Over time, the prongs on your electrical plug get dirty and also get pitted.   This causes a high resistance connection when you plug into shore power, and as your power needs increase, the plug will heat up exponentially.   You need to periodically clean the prongs on your D shore power cable.

Also, perhaps you have replaced your shore power plug with an aftermarket plug and kept your shore power cable.   In this case, you also need to periodically check the screw terminal connections inside the plug to be sure they remain tight - especially if your plug gets hot to the touch.