Meh. I'm highly skeptical of these stratospheric MPG claims, particularly for the 3.5. I drive like an old grandma and it's tough for me to break 16 MPG. Of course, most of my trips are short city trips but even on the highway, 18 is the best I see on a regular basis.
The only way I can figure people are getting 20+ MPG on a regular basis is that they have a long commute that features a lot of freeway time, is relatively flat and there is no wind. Any kind of stop-and-go, any kind of climbing, or any kind of wind will knock MPG down quickly, at least that's my experience.
I'm on a couple of FB groups and people on there are always bragging about 20+ MPG numbers. I can't help but wonder if most of them are running 2wd trucks on factory tires and driving 50+ miles of flat, windless freeway every day.