My wife has a V6 Dakota. My friend has a V6 F150. Both trucks get pretty dismal mileage. The V8's that are available for either truck return the same fuel economy as the V6's do, because the little motors have to work so much harder to get the job done.....and they have way more jam for when you need the job done, like pulling something.
I'd shoot myself if I had a 3000 lb, 4 banger truck and it ever showed me 13L/100 kms unless it was towing a house up a mountainside....and even 9.5L/100 kms if driven slowly, I assume you mean that's empty, no payload, no trailer? You think that's good? What if you put 1000 lbs in the back? How would that effect economy? A V8 wouldn't even feel it.
My van is 8500 lbs empty and averages 12L/100 on the highway while hauling a trailer and 5000 lbs of whatever.......has the capacity to move 15 human beings and a trailer full of anything you'd like. Do I do that? Nope. But I could.....And I have put 5 human beings and 2 motorcycles inside, and 3 more motorcycles on a trailer behind it, and driven a few thousand kms like that. Bonus is that the fuel economy remains almost constant, becasue the van can do this kind of work easily.
I would never buy a truck that can barely do what I think I might want it to do regularly...I'd buy one that can do way more than I suspect I will usually need it for, because trust me....once you own a truck, you try some dumb **** once in a while when loading it up.