I have an '07 and it does the same. I thinks it's the fuel tank. The lean gets more noticable when I fill it up.
You might wawnt to reclaculate the 6.2 X 18 thing. The correct answer is 111.6 lbs. Not enough to make any part of a jeep sag.]
Maybe It's my perception, but it seems to be more pronounced with a full tank of full. For S&G's I'll wait till my tanks, empty, measure the jeep, fill the tank, and re-measure. I'll post my results