Looking at 2 trucks for an economical run around truck. I have a big diesel, so it won't be towing. Just driving around 80 miles a day, and light farm chores.
Want something that will get good gas mileage. Both trucks are reg cab short box V6 autos 2 wheel drives. One has the 3.55 regular axle and the other 3.73 limited slip. Which will do better on fuel and shift less on windy days as I'm in SW Kansas and today we have 35 mile an hour winds.

 

You'll be fine with the 3.55, I was in the same situation a few months ago and am glad I went with the 3.55 regular axle. A bit more efficient than the 3.73, and the 6R80 transmission does a great job of making up for the limited benefit of the 3.73s gearing. This may be contrary to the biggest and baddest mentality that often rules there boards, but trust me and get the 3.55. And you won't have to worry about replacing clutch packs like you would with the 3.73 ls!

 

3.55's should be all you need.

 

The problem with the 3.55 gearing is it limits your towing capacity to 9800 lbs. or less depending on if you get the 4x2 or not. The only way to get the maximum towing is with the 3.73 gears.

 

IMO it's a toss up. The traction control does wonders with an open rear. Stuff all over youtube that proves that. The MPG difference is not that much compared to the two. I have a 2010 Supercrew 4X4 w/ 3.55 LS. I bought the truck used. I wished that it did have 3.73's for the simple fact of on the interstate. It is tuned and that has helped a lot in the "hunting" of the right gear. With that being said it still drops to 5th very quick even with the tow / haul turned off. I think 3.73's would stop that. All of that being said, I like the 3.55 / 6 speed set up. It is a huge improvement over my 2002 5.4 / 4 speed auto.

 

FWIW, my '07 Mustang GT originally came from the factory with a 3.31 rear gear, but the original owner swapped in a 3.73. The dealer's window sticker said it was supposed to get 14 city and 26 highway MPG, but I'm seeing 20 MPG around town, and the highway mileage suffers at only 22 MPG. Since the Mustang will see over 90% of its miles around town, I'm happy, but if your F150 is going to see predominantly highway speeds, I'd suggest the 3.55 gear.

 

The OP stated he wasn't going to tow with the truck.