Two possible issues that jump to mind.
1. Will 18" wheels clear the brake calipers?
2. Will 18" wheels effect the tpms warning system?
1. not an issue if you follow recommended manufacturer offsets for the rim width, don't screw with offset much or you could have this trouble for sure. if you decide to run the super wide tires, then any portion beyond the fender wells becomes a ticket waiting to happen without adding fender flares...
2. tire pressure monitors, tell pressures. should work fine and are able to be transferred with stems to new rims.
concerns to me are associated with computer and OD of tires toward all truck functions, ie MPH, shift points of engine functions ect. your computer is measuring all these constantly and if they disagree from internal map you will have troubles (at least how it has been explained to me in past). there are ways to reprogram your vehicle so it knows the tire size that I would look into if you run a different size from original.
oh if you have chains, remember they prob wont fit anymore also keep spare/rim in mind of same OD....
that's all I got...