I've got a 13 F150 with the 3.5 EcoBoost (twin turbo version) and I get 20 mpg's with it on flat, straight hwy runs keeping it below 70 mph.
When towing, it drops to around 9-10 mpg at best.
I know you said you don't have the turbos, but that sounds kinda low all around for a smaller, lighter rig as yours compared to my #6000 truck when it's empty.
Maybe those Exploders are heavier than I think they are?
Good luck! Mitch
2013 F150 XLT 4x4 SuperCab Max Tow Egoboost 3.73 gears #7700 GVWR #1920 payload. 2019 Rockwood Mini Lite 2511S.