Hey 2011Tahoe! Here's my latest update, but long story short I'd still recommend the tune because of how well the Tahoe drives. Justin confirmed It IS the TCM Tune that is causing the MPG drop. It's holding the gear longer bc of the higher shift points. Justin is sending me a new tune that is a mix between the modded and stock TCM tune shift points. He said this is rare to see fuel economy decrease and is bc of my particular driving style. That makes sense, bc my wife and I are very light on the throttle. Most driving is in town at lower/varying speeds. she drives it to and from work and to pick up and drop of kiddos. It is the in-town that's killing the fuel economy. I'm in process of running another 2 tanks thru it on the modded-TCM Tune. With primarily HWY and a little in-town driving, the fuel economy has been great! 17 MPG! But it is starting to drop into the mid 16's and is now currently at 16.2. This is at 3/4 tank.
I consider myself hypersensitive and very in-tune with my vehicles I drive. With the Tahoe I am often making small adjustments to my throttle input to change the shifting and keep it in or out of v4. With the tune, If you're heavier on the throttle it actually improves the fuel economy bc it shifts more quickly into a higher gear and leads to less energy wasted thru the torque convertor. We noticed that when we adjusted our driving style to be slightly heavier on the throttle. On the hwy the fuel economy really shines.
Either way I still recommend the tune. It really is a world of difference! Obviously I'd like to have my cake and eat it too, but IMO, having the tune is worth the sacrifice in fuel economy in my case. I'll update everyone again when I finish my 2nd round with two tanks with the current moddedTCM tune, and one with the adjusted tune Justin is sending me.