The LX seems to do better on MPG bone stock. I never saw much over 17mpg back when I was stock. Better aero maybe?
I've tried to think of logical reasons. It was driven 90% highway by the previous owner, always synthetic oil. I think the engine is just very, very well broken in as a part of it perhaps. Stock all season Michelins. It was a very pleasant surprise, even back when gas was cheap when I got it. 20MPG is good for highway for ANY large heavy BOF truck. City is still horrendous, there's no anomaly there lol. V8 is worth it even with $5 gas.