Yes, it's a smaller tank; 26 gallons, IIRC. I've never had the guts to run mine past where it took about 23 gallons.
Some trucks came with 17" wheels. The tires are probably lower profile so the same diameter.
23 mpg might be a little optimistic, but I can get about 21mpg at 65 mph on fairly level ground (east coast driving). YMMV...
The Constitution needs to be re-read, not re-written!
If you can't handle Dr. Seuss, how will you handle real life?
Current oil burners: MB GLK250 BlueTEC, John Deere X758
New ride: MB GLS450 - most stately
Gone but not forgotten: '87 F350 7.3, '93 C2500 6.5, '95 K2500 6.5, '06 K2500HD 6.6, '90 MB 350SDL, Kubota 7510