I have a 99 F 250 V-10  with 4:30 gears .

Pulls like a tank . Mileage is 11-13 mpg hooked to the trailer , or running empty . doesnt really matter

Howdy & welcome to the forum! 

I have an 03' F350 dually with the Triton V10 6.8L gas engine, auto transmission, crew cab, stock components, 3.73 rear end (I think), 8' bed, 4x4.  I get about 12mpg just running around empty.  I just got a Dream Coach custom designed GN 2+1 horse trailer, about 34' total length, 8' wide.  It tows great and on level ground you'd be hard pressed to know it was back there (until you look in the rearview mirror and all you see is trailer).  Running the hills, you know it's back there, but the truck can handle it. 

For my trip from Purvis MS (where I picked up the trailer) to MD, I averaged about 6.5 MPG over the 1,000+ miles, going up and down hills on the interstates.  I improved my mileage significantly by dropping down from 70-75 MPH and keeping a steady 65 MPH.  I only put it in 'tow mode' when I was going up or down steep hills, then it was back to 'normal mode' and 60-65 MPH.

Oh yea, the cost of regular gas is significantly less than diesel, so that's one good point for the V10.

I'm thinking about getting a K&N cold air intake and replacing the stock air intake & filter.  The ads say that will increase HP & torque.  I've also considered getting one of those chip programmer units (HyperTech Power Programmer III or SuperChips Max Micro Tuner) to change the settings on the computer control chip.  Mr Truck has an article about that on his site.

One thing I have found true is you will lose significant gas mileage without saving money by using the ethyneol (?) blended gas (sold a Pilot stations and others).  I tried a tankful once, and went from 24 mpg to about 17 MPG (different car).  So I stay away from anything but 'regular' 87 octane gas.

Bottom line, I love my truck!  In a few years I may consider trading it in on a diesel if I find that it just makes more sense.  Bear in mind that I kept my original truck (GMC 1/2t) for almost 30 years before I sold it and bought this one, used.  I couldn't pass up a 2 year old F350 with less than 6,000 miles in immaculate shape for about $20,000 less than a new '05 F350 w/ diesel.  I am just under 20,000 miles total, so still kinda breaking in the engine.

Hard numbers:

211 days; 15,472 miles; $3,508 for 1,446 gals; $22.67/100 miles; averages out to 10.7 MPG overall empty & towing.

Steve

Hmmm.....not sure of the cost of the Ford options but with a Dodge the Diesel upgrade is $5500.00 over the Hemi. That puts you way ahead on the cost/milage issue....2500ish gallons of gas to burn or 25,000 miles at 10 MPG before the mileage issue becomes a factor. IMHO 

Actually I've done all of the above. And thats how I got rich! I know what the maitanance of a gasser vs deisel is. It was a no brainer when deisel was $.50 cheaper than gas.That is a $1.00 spread. Lets see insurance....Oil....filters.... just hope big time you don't have a real problem like an injector pump or a tubo. Don't get me wrong...I drive a deisel..and love it! But I do know gassers are cheaper to maintain, insure, and repair. If we never have a problem or fuel gets higher we win. But in my opinion there is a lot more to it than the MPG factor. 

First, in Indiana right now diesel is from 2.39-2.50 w/tax and 87 octane is running 2.28-2.40. Now, as for the initial cost of the diesel, you just said you were going to put a banks kit on it. So your going to add several thousand dollars to the price of the vehicle and that brings you close to just buying the diesel option to begin with. Now, as for maintenance, the diesel IS more expensive when you need it, but you don't have as much mintenance as a gasser to begin with. Yes, oil and fuel filters, but never a spark plug. Speaking of spark plugs, that was the weak spot of the V-10, and unless they have redesigned it you might have an issue around 75k miles where the threads blow out. They apparently didn't put enough threads in the block, and there have been many instances of this happen in the last few years. Especially in heavy use vehicles. That being said, I still like the V-10, but I prefer my Powerstroke.

We are both right. I looked at it if you buy the gasser you can put the $5,500.00 in your pocket to buy gas! You figured how long I will have to drive my diesel to get back my $5500.00. I never figured it out! now I know! 

To the rest of your questions....How heavy is your load. How often will you use it. Will you use it as you would a car, town trips etc.? What is the terrain, elevation like that you will use it the most?

I drive a '99 F250/SD V-10 auto and it's fabulous.   I bought it used w/ 15K on it back in '01.  It is just 2 wheel drive and I did get stuck once driving into a soft, muddy fairground lot.  Since then I pay close attention to where I turn into for parking.     My milage is much like the others, 10-12 when hauling and 15-17 on the highway sans trailer.  In town it drops back down but hey, it's just money!

Mountains are your main issue with getting good mileage outta that gas engine.  I think you'll be well under 10MPG on mountains if most folks are getting that towing flat.

I used to tow with a gasser and big hills KILLED the mileage, like cut it in HALF!

Y'alls mileage isn't too bad.  I was getting 12-13 with my '91 F-350 diesel at 70-80mph with the horse trailer; 30' gooseneck at 10,000 pounds.

Next time I tow, it will be interesting to see how mileage improves when I slow down a bit.  On the hills, believe me, I was I had a newer V-10 or diesel.  If I were buying now, and the truck HAD to be a Ford, I'd buy the V-10 over the 6 liter diesel.  Especially with the towing mileage y'all are getting vs the towing mileage of the new 6.0 and diesel fuel prices.

Let's compare towing mileage of the gasser vs towing mileage of the diesel.  They seem pretty close to me from what I've read here.

Just wait till you start having to pay to keep that diesel on the road.  THEN you'll appreciate that gasser.  I can't believe how expensive diesels have become to operate/maintain.  Parts for my '91 Ford IDI diesel are affordable.   couldn't afford to own a new diesel truck once the warranty ran out.  Besides, with the enviro-freaks on patrol now, they've screwed up diesel engines big time with EGR.  Durability and fuel mileage of diesels are not much, much less than they used to be.  Soot being redirected back into the engine is not good for engine longevity.  Dirtier oil full of abrasive soot.  Bad stuff.