Welcome aboard. I would say that it is the taller tires and they will need to be run with a few more PSI that the XT would.
It is disappointing that the tire pressure was 5 PSI if that is the way you received it from your dealership.....their bad that could have caused your mis-handling......it should have been per the manual, then up to you to vary from then on.....did they fall short on the prepping of your machine anywhere else that you have noticed?.......LanceI felt the same thing in my X when I got it home. So I started playing around with the tire psi and I dont know if you guys have checked the owners manual or not but they recommed like 10 front 12 rear for the minimum pressure.
Mine was set at 5 all the way around and aired them up to 12 front 15 rear just to see what would happen and it made a WORLD of difference in the body roll.
I plan on playing around with the pressure some more and adjust the shocks and see what happens, but I am pretty happy with the way it handles for now.