Sorry NoCal, I'm still new to this but what does the aftermarket gears do? Will that improve MPG by pushing heavier tires I'm assuming?
Larger diameter tires, change the gearing, so a higer ratio, (lower gears), will return the power and keep your torque converter locking up at the correct time.
The power loss isn't a big deal for many, because the Titan has a lot of power, and the other modifications like exhausts, headers, tuners, etc, can make up for the added weight of most tires, and higher overall gearing.
Btw, the higher overall gearing could give someone that drove on flat freeways, for long distances better gas mileage.
But the torque converter lockup issue can only be addressed with aftermarket gearing, (or smaller tires). I get hessitation of going into overdrive with my 34's, but didn't with the 33.5's. It's pretty mild with my Big Tow 3.36 gears, but with the non BT 2.94 gears and 35's you can drop out of OD on just slight hills. So for mixed driving most will get better gas mileage with aftermarket gears that return the overall gearing to near stock, because their OD is working when it should.
I plan to drop to a smaller diameter since there aren't gears yet for my 4x4's front differential, and the one's most likely to be released first, are too high of a ratio, (4.10), for 34's and 35's IMO. If they are too high you get more power, but worse mileage. I would like something in the 3.55 to 3.73 range. If I towed a lot in the mountains, the 3.73.