Mine worked well just last weekend on a long grade downhill, towing a trailer. Kinda took me off guard, then I remembered reading or hearing about it.

 

and if you tow heavy you may have to manually downshift more and run it close to red line. As much as I love my 3.5 ecoBoost for the power and torque, the lower displacement means less effective engine braking (It's just physics) You have to make up for it in RPM. I'm just manually doing what a "Tow Tune" does.

I just towed the "Ike" this weekend downhill with my approximately 10,000 pound fifth wheel form Eisenhower tunnel to Silverthorne took me 8 brake applications in 3rd gear @5000 or so RPM. Same story coming down Fremont Pass and along the I-70 corridor from Copper Mountain to Denver. Uphill was just over 9:00 minutes (I hit some traffic as I don't have a chase vehicle helping me out on lane changes like the TFL Truck guys do.)

FWIW ALL Gasoline engines can "engine brake" going down hill, all you have to do is down shift, let off the gas and let the engine compression and gearing do their job. Engine braking is nothing more than down shifting and attempting to use engine compression and gearing to "Hold" the truck. Diesels are an entirely different story and do require some additional engineering to "Engine Brake" typically only found on commercial engines designed for it. Diesels are usually configured to use "Exhaust Braking"

 

My 2011 Chevy does not need tow haul engaged for grade control to function. GM does not recommend tow haul unless the total vehicle and trailer load exceeds 75% of the GCWR for the truck. Something that most people would miss is that with the GM system the transmission needs to be in Auto mode. If you put the transmission into Range Select mode to change the gears manually then the grade control is shut off completely. With the Chevy trucks the grade control integrates the exhaust brake on the diesel engine and its operation is seemless.

Tow haul mode if quite different with the F-150 where it needs to be engaged to have any engine braking in effect on a downgrade. The GM approach is much better but the F150 is better than nothing.

 

I had a 2020 Sierra, i never noticed the grade/ engine braking kicking on while towing. I dont think it had it. Granted I only had it for 2500 miles before trading for my f150.

 

My 2019 does in tow haul mode. I'm actually surprised at how effective it is with the 3.5 Eco, I tow in the High Sierra on windy steep roads, I expected much less effect.

 

Displacement does determine the amount of natural engine braking you get, but we don't get all of it due to cam timing and lift. VCT adds the ability to create more resistance, using more of that capacity. The difference isn't stark, but you ca see the pre-VCT V6 trucks gain momentum faster.

 

Compared to my Previous 5.7 liter V8 towing the same trailer on the same section of roads and downhills, the difference is noticeable. IMO grade braking using the ecoBoost with the 10 speed is different and not as effective as a larger V8. To compensate you need to downshift early and let the engine rev.

As stated I love the ecoBoost and it is a very capable engine but it does have limits and grade braking a heavy trailer is one of them. Remember I am towing a 10K fifth wheel in the rocky mountains with an HDPP so not typical duty for this class of truck.

Next truck will be an F350 SRW short bed (so I can fit it in my garage), have not decided on 7.3 Gas or the 6.7 Diesel availability, price and new trailer will help me decide that. Started online shopping already. Really liking the GD Solitude 310GK, and Alliance Paradigm 310. I want to keep it under 35 ft as I like Forest Service and National Parks.

 

The 5.0 has 40% more volume and 10% more compression than the 3.5eco. Can't get around that, but some trucks that have variable vane turbos can close the bypass and adjust the vanes to provide additional drag. Those are more expensive, less dependable turbos, though.

 

Another feature of Fords Tow/Haul mode is it re-programs the shift point (stays in lower gears longer) as well as keeping the transmission engaged when coasting in order to take advantage of engine braking.
And....can your Chevy do this...

 

I'm of the same view as TerryD64 - I tow about 7000lb frequently in the Rockies and the Oregon Cascades with my 2013 XLT and while the 3.5 eco is outstanding on the way up the grades, it doesn't generate nearly as much confidence on the way down.

Running the air conditioner compressor on the downhill grades helps a little.