In all probability, 305/50x20 is the largest tire that you can install without rubbing. That's what I run on my 07 Yukon XL Denali. I run Michelin Defenders, as I do very little off-roading, but I want a tire capable of navigating the NH climate year round.
To be sure:
Regarding wheel/tire combinations that will fit your truck without rubbing, no 2 trucks and their suspensions are exactly alike, due to a number of factors including accumulated wear on the suspension components and different wheel widths and offsets, so there is no guarantee that what fits with no rubbing on one truck will automatically fit with no rubbing on your truck. Other folks' experiences can guide you in one direction or another, but the final test will be when you mount the wheel/tire combination on your own truck.
To assist you in getting a good idea on whether or not specific alternate wheel/tire combinations 'may' fit your truck with no rubbing, I recommend that you use the wheel/tire comparison app at the URL listed below. You can use this app starting with your existing wheel/tire combination as a benchmark, assuming that there are currently no rubbing issues with it, and measure the actual critical fender and suspension component clearances as directed by this app. Then, you can enter alternate wheel/tire combinations, and this app will give you the projected changes in these critical fender and suspension component clearances.
https://www.wheel-size.com/calc/
I used this app for determining whether on not I could use my current alternate wheel/tire combination, and it accurately projected the changes in critical clearances. Again, the use of this app in not an absolute guarantee that an alternate wheel/tire combination will fit without rubbing, but it provides a much better assessment, or projection, than simply an educated guess on your part, or a statement from others that it worked on a truck other than yours.
