If your 4wd and do the 3" spacer then don't be surprised when your CV boots rip open. The boots harden over the years and once the shaft angle changes it they sometimes tear. Once replaced most people get long life out of them. Just google level lift and cv boots and you'll see all the threads about it. Other than that your going to put extra stress on your ball joints. 3" is a bit extreme in my opinion and you get what you get.
2005 F-150 XLT Screw 4x4, 5.4L V8, 80k miles, side exit Dynomax Bullet, 2013 Factory black FX4 20" wheels w/ 275/60/20 Cooper AT3's, Billy 5100's all corners