Let's try this again,
 

with not so much superfluous information. In theory, which truck will provide the better fuel mileage while towing a (less than 1000 lb) load, a V6 or a V8 of the sample make? Will the difference be significant in terms of fuel efficiency? thanks.

Aerodynamic drag is going to be a far larger issue than weight, especially since you drive it mostly on the interstate.

I think the V6 is still likely to be the most fuel-efficient choice for that job. However, it sounds like you really would prefer driving the V8...so go for it.

I would say that if the difference between the two is very small, then maybe the V8 would be better since it does help the resale later on. you may also get better creature features with the V8 since it may be offered only with an upgraded package.

I think the V6 would probably do better. very rarely does a smaller engine get worse efficiency. it does happen but not too often.

I believe the Escape hybrid has 1000# tow rating, but I'm guessing you want to stick with a 1/2 ton truck.
All else being equal, the V6 should do better. A manual will give more control, but the latest gen of trucks have 6 speed autos. Then there is the design age of the engine. I've noticed the newer, larger V8s get about the same as the older, smaller ones, maybe even slightly better. Then there is a rumor Ford will be putting the ecoboost from the Taurus SHO in the F150.

There are also 4cyl. 4x4 trucks available.

I'm pretty sure the Escape is FWD (unless you get the AWD version of course). Launching and landing a boat doesn't work well with FWD.

That's a good point though...there's plenty of more efficient vehicles rated to tow that load. You will still want something relatively long and heavy for stability.

Yeah, a 1000# trailer isn't really a strain for most trucks. The 2000 Ranger manual had the following tow ratings; 4cyl - 1 ton, 3L V6 - 2 ton, and the 4l V6 - 3 ton. The ratings were actually a smidge above that for the 4x2, with the 4x4 slightly lower.

In the case that the load is at the top end of the smaller engine, the larger engine might get better fuel economy do to using lower revs. But it comes down to specifics. I've seen a couple of claims that the Ford Vulcan 3L actually got better economy at 3000rpms. Never could test that claim with an automatic though.

I would not want to tow 6,000 pounds with a 2000 Ranger no matter what it has for a powertrain, unless we're talking about a 6,000 pound pallet of bricks on a dolly with good brakes...

yeah, that sounds like a bad news. But I wouldn't want to drive a 2000 Ranger w/ or w/out a tow load ;)

Back to the V6 vs V8 I can't seen any way you would save with the V8. The only way you could save is if the V6 was so under powered that you had to have it in lower gear most of the time.
But that said, I'd probably go for the 8. I just don't like V6's that much, 4 or 8, they just sound better... I'm okay with strait or slant 6's too.

I thought at 5000 pounds you were required to have trailer brakes. At least here.

While the 3L is rated by Ford for 4000, the class III hitch I had on it was only rated for 3500. I don't suggest going out and testing it, but I'm wouldn't surprised the posted ratings are on the low side by a fair margin for CYA purposes.

There may be state laws about trailer brakes, but I bet the first limit you hit is manufacturer's requirements. Ford probably requires brakes above 1000 or 2000 pounds.

Late-model tow ratings seem to be immune from the manufacturer's legal department. They tend to be optimistic, where you could tow the max if it's a very stable trailer and you're not going far. Also, the vehicle's tow ratings are calculated for completely stock vehicle with just the driver; they subtract curb weight + 150 pounds for a driver from the GCWR and that's the tow rating they provide.

In 2000 the tow rating competition ("Our half ton pickup can tow a million pounds!" "Well ours can tow TWO million pounds!") hadn't really heated up and they were a bit more realistic than they are now. By 2004 the manufacturers were one-upping each other every year.

Remember that if a crash happens and you have violated the manufacturer's instructions (manufacturer of any of the vehicles/equipment you're using) or any laws, you may end up at fault even if you didn't cause the accident and your insurance company may not cover you.