Al Kohalic

I have Screw 145' Eco 4X4 with 3.55 and it tow just fine. I recently towed 4,500 lbs from SA to Houston a few months back at it didn't even budge from 75mph going up the hills. It only downshifted into 5th grear once on a grade 3 hill. The 3.55 and 3.73 have the same max towing capability at 9700 lb 4X2 & 9600 lb 4X4 unless you get the max tow package which is 11300 lb. That info is found here http://www.ford.com/trucks/f150/specifications/towing/. The 3.55 will net a better mpg then then 3.73 if driven identically unloaded but not much. I have driven both and cannot tell a difference at all in acceleration and towing. With this much low end torque in the Eco maited with the 6R80 transmission, the two rear gear ratios will be hard to tell apart unlike other engines where it was more noticable. With the amount of weight you will be carrying, then you probably could not even feel the difference. It pretty much comes down to personal preferance. If you need more info on how well the 3.55 tows then read this article http://news.pickuptrucks.com/2011/04...-6-part-1.html. Both Ecos are 3.55 with one pulling 9,000 lbs up and over the mountains. Hope it helps. Don't feel bad, it took me weeks to decide which gear to buy.

Edit: Also, if you read the pickuptrucks.com review you will notice that 3.55 was a bit faster in 0-60. The 3.73 was 6.82 with the best of 3 runs and the 3.55 was 6.79 with the best out of 3 runs per this review.

Brambo_atx

My boat is about 4,000 lbs so not real heavy.

Brambo_atx

I have a K&N air filter and it is clean. Some of the hills West of Austin are pretty steep. Those are the ones that get me with my 5.4L with a 3.55.

Hofmanns4rj

I had a 5.4 with 3.73s in my last truck and it struggled to pull my 24' Regal boat (about 6500-7000lbs with trailer and gear) and eventually blew the seals in my transmission going up a steep grade on a hot day. Without towing it was perfectly fine, but while towing it was always kicking me between gears and for the most part I could not stay at the speed limit on freeway hills (Washington State). Truck would shift down and then if I wanted to go the speed limit the truck would have been at read-line. Basically, I hated the truck every time I had to tow my boat. Now I have an Ecoboost Screw with with the 6.5' bed and 4:10 gears - It's fantastic and I can go on any road or freeway and always maintain the speedlimit+. In short, my Ecoboost FX45 with the 4:10 gears is in a different league than the 5.4 I had with 3:73s.
I should add that both trucks had 35" tires so the 4:10's on my Ecoboost comes out to be about 3:7xx. So two thumbs up for 3.73's with an Ecoboost if you are towing heavier loads and live where there are lots of hills and steep boat ramps (like Washington State)

69428SCJ

The RPM difference between a 3.55 geared and 3.73 geared truck is less than 100 at 70 mph. There is no way that this will ever equate to a 2 mpg difference.

Al Kohalic

Sorry, I ment a few 0.1 mpg not 1.0 mpg. I changed it.

69428SCJ

No apologies needed. I drove them both as well. Same trucks different gears. Had them both for a couple of days. I thought they performed almost identically. I had to order my truck because dealers simply do not carry 6.5 ft bed SCREWS. I wanted the ELocker and really saw no difference in mileage between the two trucks.

nathan_nathaniel

I have the EB with 3.73 and hope to change it to 4.10 in the spring. I'm very satisfied with the gas mileage, so I'm not concerned about the change. I've been modifying my truck for work, and it's developed a weight problem... it's not quite as "perky" as it was.

My mods and work equipment have added about 1,000 pounds to my curb weight, amd hopefully a 4.10 rear will help bring back a bit of the jump.

EricTheOracle

It really does matter.

Kenneth Forbus

It might only be a extra hundred rpms but you constantly running that over the coarse of your vehicles life. The 3.55 will see around 19-20 mpg and 3.73 will get 17 mpg. 2 mpg extra gives you 50 more miles per tank. For me that's over 1000 extra miles per year. Anyway good luck with your choice!