I've seen 30 with 315/70-16's on a leveled 02 lb7 xcsb/4dr.
Ran over 1000 mile trip from Des Moines to Branson Mo, over to Topeka Ks, and back to DM with these 315's on stock wheels, and hand calculated at around 34 mpg. I used less than 2 tanks of fuel the whole trip. First tank had 836 miles...