Yes they are 6 on 5.5 you are correct on that. As for the back spacing you are also correct, for the OEM or stock wheels you can run a 265-75-16, but Im not sure on the width of that wheel. I think its either a 6 or 7 wide maybe even an 8 wide. I work at a tire shop and I have seen what very narrow wheels do to big wide tires, you'll wear the center of the tire down before any other part of the tire does, It's called crowning. What type of tire are you looking for: Mud Terrain, All Terrain, ect. A 265-75-16 IS a Very common tire size and come in a P-Metric or a LT. LT is what I would recommend, More load bearing and when you get off road you can let air out and still have the tire on the bead with out worrying about losing the bead. PLUS you get Much better puncture resistance from rocks, nails, ect. Basiclly, a 265-75-16 is a 31" tall tire. 285-75-16 is a 33" tall and a 315-75-16 is a 35" tall tire. that is how the P-metric system is by my understanding. 31x10.50x15 is the equivilant of a 265-75-16.