Check out this thread. First response is from someone who had the 5.4 and 3.5 turbo.
2015 - 2020 F150 - Towing with 3.31 rear end - What are you guys with 3.31 gears towing, any disadvantage? Alot of local dealers seem to order alot of these with the 3.5 eco and the 5.0.
www.ford-trucks.com
I haven't used the 3.73, and I'm sure it's an improvement, but I'm also sure it's not necessary for me since I've been towing 7K fine without it for 3 years. Very rarely have I felt I lacked for power, as I'm not driving around constantly flooring the accelerator. I don't always have the tach up in the gauge cluster, but I think I rarely go north of 4,000 RPM. I've used full power to merge or pass in heavy a traffic a few times, but you can imagine I'm not doing much passing towing 7K. Even with me traveling a max of 67 mph (trailer tires are only rated to 65), I do occasionally happen upon vehicles traveling even slower. My vehicle is rated for 9K in this configuration.
The only reason I would really want the 3.73 is if I frequently towed steep grades, and more for engine braking than acceleration. As it stands, I've towed some grades traveling between Houston, San Diego, and Las Vegas, NM and didn't have any issues. But it wasn't any Ike caliber challenge. I'm in Portland, TX right now and there was a stiff headwind on the way here. I only got 7 mpg instead of the 9 mpg I normally get with my speed between 60 and 65. The truck was in 5th most of the way, and may have picked 6th if I had not locked it out. I heard locking out the higher gears can provide improved mpg, but obviously it didn't work this time around. But I can't tell if it was because of the headwind, or my gear selection.
I dunno. 1/2 ton vehicle with 3.31 and a 5.4 won't pull much IMO. I have heard that the EcoBoost does much better, but I ain't got one of those. I had a V-10(3 actually) with 3.73 and would have rather had 4.10 in any of them. My trailer was 6000 lbs. I should mention I buy used trucks, thus used Fords!