How big of a tire could you fit with a 17 inch rim vs the 18inch that you have? Pretty cool that your dealership is cool with aftermarket suspension. How do the ridge grapplers do in the snow? Pretty sweet truck.
I ended up switching to 275/70r18 Toyo Open country III. I think a true 33.5" would fit, but in my opinion having a little more room to account for mud and snow buildup is key — hence going down to a true 32.5".
I hated to ridge grapplers for the week I had them. Not sure what all the fuss is about, sure they're quiet on the highway, but they pull at every little undulation or ridge. Not a great on highway tire -- and after all most of us spend 95% on highway.