is it better for mileage to tow with higher RPMs or lower RPMs want to get the best out of a gal of gas with these prices when I tow with tow/haul mode it generally gets below 2k rpms on hwy but I hear others talking higher rpms may be better

 

Depends on what you're towing. My 5x8 open trailer with a couch on it, I let the truck select the gear as there is more of an advantage to being in a lower gear with almost no extra drag.

Towing the 8x16 enclosed, I lockout to keep the engine above 2000rpm. It'll run just fine in 6th, but that's because of the boost, and that boost likes to suck down extra fuel.

Towing a 26ft travel trailer, I shoot for around 2500rpm, which puts the engine at the start of the rpm range where it needs the least boost to generate it's rated power. 2500-3500 are the sweet spot for my 3.5, your 2.7 will have a similar efficiency rpm range.

 

Every truck is different, and ecoboost will get better mileage with less boost and more rpm, the V8 it doesn't matter a lot and lower is sometimes helpful with mileage.

An ecoboost at low rpm and 10lbs of boost gets terrible mileage.

 

I dont think I have a gauge to see what the boost is

 

on my '19 it's buried in the menus, "settings" then "gauge selection"

 

When I tow my 24.5', 6000# TT, I lock out 8/9/10 gears, and the engine purrs along at 2500 rpm.

 

The 3.5 EcoBoost makes prodigious torque around 2200 rpm... but the Coyote 5.0 requires a little more revs. I drive a Coyote 5.0 in a 2016 XLT and this engine LOVES to climb hills at 3400, give or take. These engines were designed to endure, and endure well, sustained high rpm. I have no problem cracking the throttle just a little more and parking my tach at 4000 revs for a long, hard climb when towing my little camp trailer.

Sure, the oil gets warm but the rest of the truck doesn't even break a sweat. Granted it's 8 or 9 MPG under those conditions but once leveled out at cruise it's back to some pretty decent fuel consumption (depending on the trailer frontal area - more trailer frontal square footage equals a larger air brake).

 

You make a good point and help to illustrate the difference between some considerable boost or a little more rpm and less boost.

I am still astonished at my memory of driving a 3.5 and tipping into the throttle at highway speed (with a 6-speed) and the resulting surge in torque. Almost felt like a big rig pull.


Too, as both you and Atlee noted, knowing how to use these great 6- or 10-speed automatics goes a long way to better efficiency on the one hand and then driving fun on the other.

 

It's not that simple. For each combination of weather, road conditions, grade, (combined) vehicle weight, & vehicle condition, there is some specific engine speed that is most-fuel-efficient for that engine loading. And it varies each time the road or weather changes (including hills & curves) so you can't pick one & go with it. The engine will burn the gas it needs to get where you're going - just accept it. Towing is NOT a fuel-efficient activity, but airing up all the tires (trailer, too) to their max pressures will reduce fuel consumption (at the expense of ride quality & tread life).

On this ~1400-mile trip, I got ~6mpg:

(click this text)

 

With my 3.73 2020 2.7L towing a ~6500lbs travel trailer I let tow/haul mode decide and generally end up around 1800-2000 rpm in 8th or 9th gear depending on speed. I did try locking to 7th gear and ~2500 rpm for one hour out of a two hour sprint at 65mph and got worse gas mileage according to the truck (9.9mpg in 7th, 10.6mpg in 9th/8th with tow/haul selecting). This was gentle hill terrain so would drop to 8th for some climbs and even 7th would be required once in awhile. Was towing with 93 premium.

These days I only lock out gears is for major hill climbs to improve cooling circulation and keep my peak transmission temps at around 210-215 instead of 215-220. I target 2700 - 3000 rpm. The only other time I do it is for excessive rolling hills to prevent the transmission from shifting too often.