[Alberta's Child]

I'm not sure that's the case anymore. I was shopping for a compact car a couple of years ago, and I was surprised to find that the fuel efficiency rating for the automatic transmission was 1-2 mpg higher than for the same engine with a manual transmission.

I think the technology in modern powertrains has gotten so advanced, they actually operate better than humans.

[Paladin2]

It’s all about the gearing and the rpms that the car achieves in high gear.

Most cars with manual transmissions these days are targeted at performance, not fuel economy and get gear and axle selections based on that.

There is nothing more efficient than locking the input shaft to the output shaft.

Axle ratios to achieve that in high gear are now rare.

[Paladin2]

Also note that for decades I have regularly achieved higher than "sticker" mileage on m/t vehicles. Not so much on a/t vehicles.

I just bought a new m/t car with a 31 mpg highway sticker.

On a pleasure drive up into the "mountains" (hills actually, but with an emphasis on "up" (and then back down)) and back the trip computer claimed that I had achieved an average 42.5 mpg.

(note that my Turbo Diesel m/t cars rated at 47 Highway get ~44 at 80 mph). YMMV.

[Paladin2]

Note that the "highway" test has no speeds over 60 mph: