On my '05 the dash says 16 to 16.1, hand calculated it's about 15. I've seen a max of 16 but that was as we were going 60 mph on dead flat ground for what seemed like ever lol but it's also on 35's and at that time I had a ton of stuff in the truck.
The Prius is currently showing 48.8, heck even at 40 mpg I'm happy lol but I doubt I'll actually calculate it.
2005 F-350 Lariat, studded, Sinister diesel EGR delete, Sinister diesel coolant filter, MBRP 4" straight pipe, Banks ram air intake, SCT X4 tuner, blue spring, EGT sensor, fuel pressure sensor, 4" lift, 08 style mirrors, 35x12.5R20 Toyo RT
2006 Ford F-250 King Ranch FX4 crew cab short bed
4" flood lights for back up lights, High idle switch, 2008-16 tail lights, 2011-16 style 6.0 Powerstroke badging, Edge Insight CTS2, Blue spring mod, Viofo A119 dash cam, 275/70R18 BFG KO2, 2017 style mirrors, 2.5" lift coils, F-350 blocks in the rear, Riffraff CAC boots, Backup camera with spot lights in the rear, SCT X4 tuner, Fab Fours black steel series bumper with pre-runner guard, Mishimoto coolant filter, 4" Diamond eye turbo back straight pipe exhaust, 18x8.5 American Eagle Alloy Hardrock series 0168, 7.3L Fan clutch (Hayden 2835), Spyder LED tube projector headlights
2011 F-350 King Ranch FX4 crew cab long bed 325/65R18 BFG KO2, 18x8.5 American Eagle Alloy Hardrock series 0168, Steelcraft Elevation Bullnose Front Bumper, 20" front light bar, MBRP 4" DPF delete competition pipe, SCT GTX tuner with Tyrant tunes, Rough Country 1.5" leveling kit, Auxbeam LED headlights and fog lights, platinum style grill, black mirror lights