I had the same issue. Turned out the tank sensors were wired in the wrong order. Each sensor has a color coded wire to it which turns on a specific light on monitor panel (E, 1/3, 2/3, & FULL). Mine worked fine after Redwood dropped the front belly pan and fixed this.
Radio_Flyer, sounds like you have bigger problems. You should get your dealer involved with this one.
Mike & Pam '12 36RL, Kodiak Discs, 17.5" G114s H-Rated, SRE4000 w/HD Shackles, Joy Rider Shocks, Flex Air, 5.5 Onan, W&D, DW, 4 Scare Lights, (2) 6V Trojan T-145s; Progressive EMS-HW50C, Winegard DTV Sat, Sony/Denon 4K Home Theater, WiFiRanger EliteAC Pack, weBoost 4G-X Cell Booster.
2020 RAM 3500 Limited CC, LB, 4x4, DRW, Cummins HO, AISIN, 4.10, Curt A30 w/OEM Prep, Transfer Flow 70gal Aux Tank/Toolbox.