I have 3.91 gears out back. My next set of tires will either be a 305/45 or a 345/40, if it'll fit an 11" rim. Both are closer to 28" tall. I'm gonna switch the tire, then see if going to a 3.21 is worth it. The 3.91 might be fine with a bigger tire, I used to run a 28x13.50, but can't remember that long ago. Lol