2007 jk with 102,000 miles. I bought the jeep when it had 12,000 miles on it and it already had a 2" rubicon express lift installed. The 2 front shocks were replaced around 60,000 but the rears are original and have at least 90,000 on them. They don't seem like they are riding bad so my question is how do I know when to replace them? What is the average mileage expectancy? Are there any good write ups out there to do it myself? Thanks for any insight you can provide.