This^. Ive always done two at a time. Put the new tires on back and best two old tires on the front. Theoretically on a 4x4 driven in 2wd the majority of time the front tires are along for the ride and not under power.As long as the tread is good enough to not negatively affect your steering you want your best tires under power on the back. On an awd you it is my understanding uneven tread wear from front to back can hurt your transmission or transfer case so you want to replace all 4 tires at a time. I would certainly try to get the tire fixed if possible but if its a side wall puncture or you drove on the tire for awhile it may be shot.Two tires at a time is fine if it's 4WD. I've done it on my 05 Chevy. Might be a problem for AWD if the circumference is too different from the old and new