I have a 2007 Suburban and have a statement from a GM engineer that they tune the engines for the least drivability complaints. That better mileage is possible. I then have the frustration of finding lots of claims of better mileage from tuners but I can't find posts from consumers agreeing. I see posts where people say they ordered one but they never follow up and give their experience.
I've had a 60 Pontiac, a 67 DeVille, a 75 Monza (262 and then 307 swap) and a 99 Suburban so V8s ranging from 262 to 472 cubic inches, carbed and fuel injected, stock exhaust, ignition and intake to heavily modified. Best mileage is the 07 Sub at 13.5 mpg and worst was 8mpg with the 389 Pontiac, the 472 Caddy got 10. Yes the 3 ton 07 Sub gets better mileage than the 1.5 ton Monza did!
So I'm skeptical about improving my 07 Suburban's mileage but the way the V8/4 system works I'm wondering. I'm thinking the only way is reducing the load when accelerating from a dead stop and that would mean an electric assist motor (think Tahoe hybrid). I really think this is where the improvement needs to be made to improve the mileage no amount of cruising improvement can make up for the consumption to get the big brick going.
Anyone with experience with a tuner in a crew cab, Avalanche, Tahoe, Suburban or the GMC and Caddy equivalents like to say otherwise?