There will be a point, I suspect, that both vehicles get within a mpg of one another. Will a GX550 GET 23.5 MPG at 75mph?
At 75mph with a UHAUL 5X8 box I got 15 mpg. Probably only 1000lbs total weight. At 77 if dropped to under 14. I could feel the trailer aero really starting to drag so I backed off. Effortless at 75 in spirt mode but that makes it a bit shift happy. It would actually hold one gear higher better I Normal mode....I think. I was also getting better anticipating the hills like an 18 wheeler....