Hello out there: A dealer recently encouraged me to go ahead and purchace a F150 w/ 373 Ltd. Slip differential (which he had on his lot) which met most of my criteria besides the 355 Ltd. Slip. He said that most customers perfer the 373 because of the performance it provides and also added that most claim it gets better gas milage. Now I never haul or tow heavy and saw no need for the bigger rear end and counted on the fact that a 355 would be more efficient when the truck is light. 90% of the time... How about some opinions, expertise, and experience...

NEW F150 Buyer

 

Honestly, you will probably never see the gas difference unless you do a lot of high speed driving. I have the 3:73's and am getting 16 mpg's in rush hour LA traffic with AC. I pull at least 18.5 on the open road at 75-80 pending on traffic speed. Where it helps though is when you encounter hills while driving or when you tow, at those moments you will be glad for the those gears. Besides these trucks are heavier and the little extra gear makes it accelerate like a heritage with 3:55's.
Good Luck with your truck,
Brian

 

I have the 3.73 in my truck. I wanted the 3.55 because I thought it would give better fuel economy, but the 3.55 isn't even available on some models. I have the FX4 SuperCrew. I think you can't get the 3.55 on any SuperCrew 4x4 trucks. Some others maybe as well.

 

I have 3.55 gears on my STX and on hills my truck must downshift (sometimes twice) in order to keep up with traffic. It seems like if I had bigger gears I would actually see better mileage b/c the truck wouldn't have to downshift...

 

I've got 3.73LS in my Lariat. I'd gone for 4.10's if they offered it.. With 32" stock tires and .70 gear in overdrive the engine is running less than 2000rpms at 65-70mph.. I'm getting 15.5-16mpg around town and I've seen as high as 19.6 on the highway, but the truck only had 125 miles on when it did that. Just 700 miles now, but I've got a couple trips this week and I'm going to check it again.

 

I'm not an expert by any means but from what I gather the difference between 3.55 and 3.73 is small, its not like we are comapring 3.55 to 4.10 here. If you never tow you'll probably never notice which one you have and honestly I havn't been able to see any difference in gas mileage between the 3.55 and he 3.73 based on what people have posted but then again all the other factors make that a hard comparison. If the dealer wants to sell you that one but you want the 3.55 tell him that you'll buy that one but you don't want to pay for the option that you don't want, see what they say. Either way you'll enjoy the truck. JMHO

 

It sounds like it doesn't really matter I had to take the 3.73. That's ok, either way it wasn't going to be a deal-breaker. BTW, I thought the one dealer was blowing smoke, but it was confirmed by another dealer. And it was a chargeable add-on. Whether I paid for it is a matter of perspective, I guess. We negotiated a price based on all the stuff put on the truck, so I could say I didn't pay for it, but then I paid a little more for something else... :-)