Since I don't think anyone has mentioned it, while going around the
various esoteric possibilities - perhaps a sticky brake or e-brake has
unstuck?

The comments about not-very-good methodology for measuring consumption
are true.

Another reason for not running the tank all the way down is the good old
condensate in the fuel tank issue - far better to fill the top half of
the tank than to let it run all the way down in around-town short-haul
driving simply for that reason, with or without the fuel pump happiness
as another reason (and the water resulting may be part of fuel-pump
unhappiness).

I've gotten mileage that bad, but with a one-ton crew cab 4wd - and it
would do better than that on the highway.

--
Cats, coffee, chocolate...vices to live by