i've read many user debates and discussions here about the need for UCAs or not if leveling to 2.8 using the 5100s, but have a slightly different bit of info here. i read with interest on a post the other day, that, if i read it correctly, 4 wheel parts won't install 5100's without you installing aftermarket UCAs. today I booked my truck into a local independent accessories shop with a good rep on lifts to install 5100s at 2.1 to level. I stopped by after work as i've never seen the shop, to meet the folks there and brought this debate on 2.8's up with a service advisor and mechanic there. I barely had time to bring it up and the mechanic said, we won't do more than 2.1 on the 5100's without aftermarket UCAs due to too many popped upper ball joints. not new info persay, but from the mouth of a mechanic with good level of experience. sealed the deal for me.