The only time I EVER get a consistent 13-15mpg in our PW is staying around the 55-65mph mark. We drove to Homer from Anchorage and back (230ish mi each way) last weekend with little wind and the couple passes you go through and I think it showed around 13.5 for each direction (uncorrected on 35s). 4 adults, a tiny human, and stuff for a weekend of fun and fishing under the fiberglass canopy. Certainly could feel the softer suspension with that load, but it’s not our norm.
Most of the time with some higher speeds, or city involved… my daily mileage is certainly closer towards 10ish.
But I didn’t buy a PW for mileage or heavy towing, so I just accept it as a given truth. But even here in Alaska, unless I’m going out the Denali hwy or up the dalton, I rarely ever carry extra fuel… just know where my closest/last is and plan accordingly. For that matter, taking the PW to/from the lower48 several times, I only carry extra in winter (I would though going up through Dawson regardless of season).
All that to say… The range sucks, but it isn’t an enough for me to get a different vehicle, when it checks so many of our other boxes.