My 93 190 2.6 is in GREAT mechanical shape and I get no better than 21-22 out of it (highway travel). It's been as low as 17 with the town/commute mix.
Then again, I drive like a bat out of hell just about everywhere and haven't spent enough time at 55/60 to see how far it will go. I HAVE noticed that mileage seems to fall off pretty rapidly after 90 or so.
I've heard some claims of 26-27 out of these cars and I'm not buying it - that's diesel territory. Well, MAYBE from a 2.3 (or at 55 on the flats), but we drive a fairly heavy, underpowered (IMO) car that only begins to eagerly respond when your foot is in it at least 3/4 throttle...