I listened to one of the better known tuners,and I shouldn't have,lol. I did it with the idea the truck would be faster and honestly it never really got all that much quicker at the track,but my oil temps went up at freeway speeds while also giving me worse milege. If I was doing it again i'd stick with the 3.21's as for me they were every bit as fast at the track and at 80 mph on the freeway they were a lot nicer to live with. My local track is 155 miles away one way,and my truck is usually there every Friday night,so the majority of miles it gets are on the freeway at 80+mph,and the 3.21's were definitely better gears for the weekly drive up to the track.Around town I don't really notice any gain with the 3.55's over the 3.21's either,but then again my truck will blow the street tires off at will with either 3.21's or 3.55's.If I didn't have a ****load of money ******* in the 3.55's,i'd be throwing the 3.21's back in it,lol