For comparison's sake:
'06 E-350, V-10, 5-sp, Quigley 4x4, 3.73's, almost 24,000 mi., scales at about 6,900 as driven. I average about 13 m. p. g. mixed country 2-lane (55-60) and expressway 65-70) driving, some city, mid-12's if I push it a little harder.
On trip recently towing tandem axle trailer weighing just shy of 3,000 empty, on US 20 across central New York state still got over 10 m. p. g.
The only load I moved was about 3,000 lbs over 45 miles, so I couldn't get a good m. p. g. read from that.
The '89 E-250 w/ 351 got 15 m. p. g. consistently, not loaded heavily.
The '95 E-250 w/ 300 I-6 got 16 m. p. g. at best, loaded the same.