Change the primary gearing to an XB12. You will need front pulley and chain. The breakover year is 2008, i think.
I'm sure you can find someone who would LOVE to swap and change to XB9 gearing, as the XB9 gearing is pretty desirable to put on a 12.
You just have to be careful not to lug the engine. You will probably find yourself shifting to 4th more often to carry speed. Unless you are like mike lowery and building a bad azz engine.