You should completely load your trailer and Denali up first before you run your air ride. This way it levels out under the load you'll be traveling with.
The Blue Ox Fuse ByPass Switch for Towed Vehicles item # BX88272 you were looking at is the correct switch for your 2011 GMC Yukon XL Denali. view full answer...
As long as the hubs on your trailer are lug-centric (meaning you have lug nuts and not wheel bolts) you can easily go with a wheel replacement that has a larger pilot diameter.
Lug-centric hubs are by far the most common setup so I would be surprised if you didn't have this setup on your trailer. But if you have wheel bolts on your hubs then instead you would need to find a rim that matches the pilot diameter size.
That said, the # AM30130 you were looking at DOES have the 2.5" pilot diameter. view full answer...
It sounds like to me that you're in need of a weight distribution system, Pete. These systems use spring tension to distribute the weight across your Yukon rather than only on the rear suspension. It also incorporates sway control to help keep your trailer tracking straight behind you while you are driving on the highway.
The only thing you'll need to know to get the right system is your total tongue weight, which you can get by loading up for a trip as if you were going for real and then... view full answer...