Has anyone found anything that works to significantly improve the Ascent’s gas mileage?
Yes. Let the car run. It sounds funny, but I’m serious. somewhat 
I have learned 2 things since having mine (9 months now and almost at 12k):
1. Whoever said here to give it some time for the gas mileage to improve is right! I have seen huge improvements in the last few months!
2. The car drives itself more efficiently than I do. Even though I consider myself a very gentle driver, I can’t beat the adaptive cruise control (and it’s obviously only something for longer drives with light or no traffic). Even if I think the ACC’s braking and acceleration is more aggressive than I would, it gets better mileage.
What blew me away the most was the gas mileage recall. I have a 4000lb pop up trailer with a top tongue weight of 470lb so it’s close to the Ascents limit. Everyone said it will cut your MPG in half. Not for me, quite the opposite. At that time I was still only getting 19.5 mpg mixed urban and short fwy trips. On our first tow, I set the ACC to 57 mph and went into cruise. 19.5mpg on a 500m round trip! And it attracts a lot!
Since you’re looking at a Hybrid, I’m assuming traction doesn’t matter to you.
It has only gotten better since then. We got 26 mpg on family trips (2 small children and full car). I even got 31mpg on a recent solo trip back from the Eastern Sierra driving through LA! What remains is bad and I can echo what others have said here. Really, really SOCal city driving is disgusting and we still only get about 16mpg.
I suspect the regular Highlander would do better. The Hybrid Highlander on the other hand is probably hard to beat as others have said.
