Let me guess...you are not driving your 4runner much these days?? That was my problem with the Firestone Destination M/Ts and my G500. Since i did not drive the G500 much (once or twice/week), the Firestones developed flatspots and went out-of-balance. Not sure if it is the tire's fault or due to lack of driving...i did rotate them every 5k miles on the dot. So, maintenance was not the issue. With the BFG AT KO, i have not had this issue...yet. I am driving my G500 a bit more these days because i want to avoid this issue and because gas prices have come down a tiny bit.
BTW, Firestones are making good tires these days IMHO. They are trying real hard to get their image back. IMO, this is the right time to buy Firestone tires because i am sure that they are trying real hard to avoid another disaster.