I have a 05 dodge 3500 dually. The stock rear tires (generals) with about 43000 miles on them were getting pretty thin, the fronts are at about 25-30% left. So I went to the tire store and bought 4 new tires for the rear (coopers HT) had them installed and now it feels like once in awhile squirmy back there. I was wondering if its because of the different tire brand, I was going to pull the spare out, buy another general tire and put the new spare, new tire on the front, thus I will end up with 6 new tires. But if the ride/response is caused by different tires I will go and get 2 more coopers. What do you think??