Previously AZ required vehicles over 26000 lbs or having more than 3 axles to fuel up at a truck stop or other outlet that charged $.26/gal rather than the $18/gal at most gas station. The fine was $1000 if you were caught by an AZDOT enforcement officer. The law was changed a few years ago but the "new" stickers are apparently just showing up on pumps. I checked with AZDOT and they confirmed that a private, non-commercial RV can fuel at the $.18 tax pumps, regardless of weight, # axles, etc. However, it must be privately owned and non-commercial. If your RV registration shows the RV is owned by an LLC that you own, AZ views it as commercial and required fueling at the $.26 tax pumps.
Steve