I hate to say it, but you're pretty close to (safely!) maxed-out on tire size for those rims. If you want bigger, there's a couple of things you have to start thinking about...
1) Bigger tires start getting you into clearance issues up front even if by some miracle you do manage to stuff a bigger tire on what you have. People get around that either by leveling (lifting the front with a set of specialized struts), or getting rims that have a very large offset (dished-out), or just biting the bullet and lifting the whole truck. That middle option means you may as well just get bigger rims anyway.
2) Safety. If you have these big vulcanized balloons stuffed onto these skinny little stock wheels, the chances of a bead separation event go way up. You can go up a little, but honestly? I wouldn't recommend it.
3) You and I share one thing in common: The itty-bitty 3.6L v6. Bigger meats means lower mpg. If you're okay with that, okay, but you will notice it a lot sooner than our Hemi/diesel-driving brethren will. Fun thing I noticed recently - switching from stock Goodyear SRAs to Falken Wildpeak AT3's with a very aggressive tread managed to knock around 3 mpg off my fuel efficiency average according to the lie-o-meter... and I stuck with the same stock tire size. Now if you get bigger meats with an aggressive tread, err, yeah... expect to lose a lot of mpg.
