Absolutely.

But only insured the PIU this evening after buying some civvy wheels for it - I've barely driven it on pavement. Most of that tank was burned by my friend who was driving it back from Nashville for me (like he stole it - he was driving circles around me in the '98 Taurus, which is why we had to fill up again to finish the trip), and then a lot more of that gas was burned out at idle while I was tweaking, inspecting, cleaning, & adjusting things, and on a couple of really brief test runs on my property (10 acres) at relatively low speeds. So while I expect it to go up when I drive it "normal" (yeah, right!), I don't expect it to double.
It's hard to believe you're drawing conclusions without even normal driving cycles.
These do get poor fuel economy and it can be the sum of many parts.
1) Large, heavy vehicle
2) High ground clearance
3) Often outfitted with large, heavy wheels
4) Tires might be underinflated
5) AWD
6) Extra drag from boxy frontal area and roof rack, mirrors, etc
7) Different shift strategy for PIU, geared more towards performance than economy. They "might" also have a different battery BMS charging strategy to keep the battery topped off at a higher charge level, where the primary purpose of the BMS for civilian vehicles is to eek out slightly higher fuel economy.
Explorers, both PIU and civilian, were never the right vehicle to choose if you care about fuel economy.
My '14 3.5L NA gets around 10MPG in daytime heavy stop and go city driving, a little higher when the streets are less congested at night, and around 20MPG highway, but I live next to an interstate and take it often, but seldom long distances, seldom even 10 miles at a time so it's barely warmed up. I drive it neither conservative nor aggressive on the highway, just keep up with traffic.