The stock tires are 255/75r17 which is roughly 32x10.50. 265/70r17 is roughly 31.6x10.50. So it should feel like running stock tires. But why downsize? And I think the 3.21s are too large for the 3.8L. My stock 3.73s and 255/75s felt fine on the 3.8L + auto. No downshifting on the hwy, hills, etc.