I don't think it matters what kind of quad you buy, most manufacturers will not warranty anything with mods. Your dealer should have told you this before he installed everything. GM, Ford and most other car/truck manufacturers would not cover warranty work with after market mods either. When you think about it you can't blame them.
Any quad with your set up will break parts if you are heavy on the gas, those big tires have a lot of rotating mass and if you suddenly catch a root or a rock something is going to give, it happens to big 4x4 trucks, mudboggers, mud drag racers etc.
I would like to see what you are going through if your having a hard time in 2 wheel drive? If the grizzly is having a hard time so will any other quad especially with those tires! Good Luck and I hope you get things fixed up under warranty but if word gets out then ever swinging dick who has ever broken anything on their grizz will come knocking on your dealers door.........Irv