Off Road Taco owner on the new Trd Pro 18in wheels. You can go to 275/70/r18 with no issues. The spare will be very tight however. You can do 35's but that is the point when you have to start unbolting the crash bars and triming, spare will not fit under the truck.
X Overland put 295/70R18 on their stock suspension Trailhunter Tacos. At least I am almost positive they did no upgrades to the OME Suspension that came on their Tacos.