I would go with the stock spec tire size. The 245 is much taller than the 225 and will hurt you in the hills. They do make an LT225 size tire.
The P tire is rated at 1703 lbs at 35 psi.
The LT tire is rated at 2640 at 50 lbs. This tire will ride a bit rough but there will be less squish in the sidewall. If you are towing long distances you may want to upgrade.
LTX M/S | Michelin Tires
Steve, Christy, Anna and Phoebe (Border Collie)
1994 Classic 30'11" Excella - rear twin
2009 Dodge 2500, 6 Speed Auto, CTD, Quad Cab, Short Bed
Hensley Arrow hitch with adjustable stinger
WBCCI # 3072