Hi ScottM - Yes, 07 Rembrandt 6775M has a fuel gauge that is not reflecting reality. (Was pretty happy seeing the tank remain on Full, even after driving about a hundred miles... But after 250 or so miles, well knew 'Something ain't right!'.)
I've read many threads on different repair approaches, and have not yet tried any of them in our coach.
For now, I'm pretending we have a 100G tank, and get 5MPG - and will use a range of 450-500 miles between fill up's, when we get out and get some real seat time travels this year. Due to our limited miles since we bought her, and timing on topping off before stopping for longer stays and or storage, the most I remember in the probably 7-9 fill up's since we've had her - is a little over 80 gallons. Along with the 450-500 range on a pretend 100G tank, I'll track our generator usage (Using the High Load 1.2G per hour.), for calculating reduction of available miles to drive.
We took about two full years to sort out and get our 04 Allure into a known baseline maintenance level, and learn her habits. We had 3-4 months with the Magna last year, but self isolating our a site we have at Pacific Shores. And due to scheduling issues earlier this year, we've had about 6 weeks total usage in the first 5 months of the year.
Fuel gauge is on our list, and I too will follow this, and other, threads on the subject closely
And, will ask around if my era 07 could have the bad fuel pick-up leaving too many gallons unavailable... (Does anyone know what year the higher fuel pick up impacted?).
Best to you, and all,