2 tanks in a row, with great results.
I got 36 mpg in Denver freeway commuting. I rarely go above 65, part of the commute is a 55mph speed limit.
I have to concentrate on throttle control, here's what I do:
1. only move the throttle plate if I need to. constant throttle position is key
2. speed limit
3. I shift from 1st to 3rd to 5th, or from 1st to 2nd to 4th to 5th. This is always done under light load, constant elevation, not lugging the engine or otherwise loading the drivetrain. If I need to move I shift normally. The onramps I have to use are very long so I don't need to max accelerate. I'm also not driving like a grandpa being a roadblock while accelerating; I usually accelerate faster than the SUVs that everyone in Denver drives.
I commute 50 miles/day, about 38 of those miles are mostly constant speed freeway around C470 on the southwest side of metro. I couldn't believe the mileage numbers, but I've repeated it for 2 tanks. 9 gallons and 325 miles for the last tank. This is with 85 octane fuel.