Do I really need to replace all 4 tires

This really depends on a few factors. As your vehicle is an "All Wheel Drive" vehicle, if you have dissimilar tire circumference from one tire to the next, you could cause an abnormal load to the transfer case of the vehicle, which can in extreme circumstances result in damage. But, at 5,000 miles, I would consider the variance between an original tire and a replacement tire nominal, and a low risk situation. I would definitely ensure that you acquire the identical tire that is being replaced for proper sizing and fitment and tread pattern compared to the remaining 3 tires.