What a friggin' difference!
So, I just drove my Jeep back from Adrenaline Offroad after having my 3.21s changed out for 5.13s. It was 20 miles door to door in stop and go traffic on back roads. The max speed I reached was about 50mph.
It's incredible. There's a massive difference in power and performance. Necessary or not, I'm going to abide by the break-in theory. I'll have a more detailed review by the weekend. It's actually going to take me a bit to get used to the difference.
Initial impression ...if your even considering doing this (35" or bigger tires and gears), DO IT!!!