FWIW - my inlaws have a 2023 F150 4x4 supercrew short bed 3.5EB that is completely stock other than a 1" front spacer "level" kit installed by the dealer. On a recent 900 mile round trip from Montana to Utah and back (hilly, but not extreme) it returned 26mpg one way and 24 back on the dash and by calculation at the pump. It was generally favorable conditions with good weather, low traffic, etc. It's very fuel efficient. I think the overall average mixed driving so far has been around 19-20mpg. That's about 50% better than my Tundra. And the F150 cabin layout is significantly nicer to use, visibility is great, highway comfort is better, - all around it's a better truck to drive. The hesitation I have is ford build quality and long term reliability. I'll still take my Tundra, but I can't deny that the F150 does a lot of things better.
The secrets I see are a combination of:
Aerodynamics - I think Ford puts a lot more effort into low Cd than Toyota does.
Light weight - a '23 F150 4x4 supercrew weighs 4,752 lbs. <- that's less than a 4Runner by about 50lbs vs a 4x4 4R model. It's ~1300lbs less than a Tundra.
It has light weight low friction powertrain. - The powertrain is closer in size to a Tacoma than a Tundra. The scale of powertrain parts is quite small - for example this is the transfer case drive chains for the 3rd and 2nd gen Tundra vs the F150. The F150 is closer to a Tacoma:
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And the other key factor is Ford runs its engine leaner on AFR. The tradeoff is hotter EGTs, hotter turbos, overheating on hot summer days towing is common, and the EB engines have a design life of 150k miles, where Toyota would design for more like 300k miles. Ford opts for better fuel efficiency in trade for shorter engine life. Toyota chooses the opposite.
When you add all of those factors together you can get a pretty significant increase in fuel economy.
I think Toyota took basically a decade off from any meaningful engineering efforts on its BOF models. And it really shows. The current lineup of new products should have been on the market around 2017 and we should be into the next generation after what we are seeing now. I think that's part of why the TTV6 is so inefficient. It hasn't had 15 years to develop and refine like the EB had. And the same for Toyota's v8s. Toyota never put any effort into improving the efficiency.
One interview discussion I found interesting and unfortunate was the discussion of the current Tacoma and its poor drivability. The engine engineer talked about how in the 3rd gen tacoma the design teams had metrics to reach and there was no metric or goal set for actual drivability. So, the engine team chose an engine that, on paper, had the most fuel efficient output for the power needs, and the transmission team had a different goal, etc. The result was an engine and transmission combination that is poorly matched to the vehicle and the engine is so marginally adequate that it has to constantly shift to maintain speeds. Plus it doesn't get very good mileage. It was just poor management at Toyota. There's really no other way around it. The silver lining is that they recognize the failure and have made an effort to correct it in the next generation Tacoma and likely also the LC250 and other products.
At the end of the day - I think a lot of factors add up, but probably the biggest issue is simply that the V35A is not very thermally efficient. The power is great. But it doesn't appear to be a good engine for fuel efficiency in any of the current models.