Not that it’s the best, but Edge does make a tuner for the Lbz. https://edgeproducts.com/shop/diesel-evolution-cts2-ca-edition
https://edgeproducts.com/shop/06-07-6-6l-lly-lbz-juice-w-attitude-cts2
I know you want to keep the 20” wheels, why not get the right wheels for the truck and remove the spacer/adapter? Might be able to find a factory knock off even.