I installed a 1.5" level in front on my '06 4x2, and the ride got really stiff. Going over speed bumps was nearly a stop and crawl event. Changed to some Rancho RS5000 and the ride is back.
http://www.ramforumz.com/showthread.php?t=100815
http://www.ramforumz.com/showthread.php?t=100815