@ktm525 I've had the 255/55r19 Goodyear Duratrac on before these issues started to occur. In matter of fact, I was averaging well above 16 mpg and getting around 20 mpg at best. I don't believe the the tires are at fault. I rotate them and fill them with nitro air at least every season, except when I have to air down and fill with regular air from a Viair 400P.
I should also mention that I had the rig flash "Restricted Performance Warning" on 3 separate occasions without any codes. Once during a normal day on a uphill freeway climb, once at night on a flat freeway, and once going downhill at night on surface streets. As soon as I pull over and stopped the car for 10 seconds, restarted, and all is normal (no codes). Since the first time, I keep my i930 code reader in the rig.