Back in the late '80s and early '90s, I had a couple of Camaros (an 86 and an 89) with the 305/OD setup, which would give me a relatively steady +-31mpg on the highway, which I did a lot living in NM. A friend had a similar Firebird, but it had a v6, and he complained that he could never get better than 26 or so.
Two things: I had a "sweet spot" drivetrain that had enough power that it didn't have to work very hard for my driving style, and speaking of driving style, he probably wasn't quite as light on the accelerator as I was.
Those cars wouldn't win any races, but they were pretty darned good road trip cars. The hatchbacks had lots of room, even able to close on a completely assembled tandem bicycle I bought for my parents. Yeah, the front wheel was resting on the dash.