4.56's and a Detroit in a 2017 6 liter 2500HD
 

Did a write up over in the HD section of GM-trucks on this so I thought I would post here as I get close to having it all done. I will post the threads link here in case anyone else wants to do something similar. If you try to just go out and buy aftermarket parts for a 2015 and newer you hit a wall and there is little to no information. BUt luckily it's the same diffs still as a 2011-2014 equivalent truck so it's not too bad.

Mine being a 6 liter makes the back the good old 10.5" GM Corporate now made by AAM. Handy how stuff never changes with GM... parts from 1973 will work in this truck lol.

Re-gear and Detroit Locker in a 2017 2500HD 6 Liter - 2015 / 2016 / 2017 / 2018 Silverado HD & Sierra HD Accessories & Modifications - GM-Trucks.com

I should be getting it all wrapped up shortly as I will go to work and use the press to get the carrier bearings mounted and then I will drop in the locker and torque down the ring gear. Should make a noticeable improvement not only from the ratio change but to going with the Detroit. I have one in every other truck listed in my signature so it wasn't right this one didn't lol.

I read most of it and got to your last post on page 5. HP Tuners does have the auto scale for the transmission, you just have to click on the right spot.

Click the edit tab, then gear/tire wizard. Plug in your new tire size and gear ratio, make sure the speedo and transmission scale boxes are checked and it will do it for you.

Well thank you. Now all I have left to do is redo the ones that are too early which a good chunk are.