REPLACING UPPER CONTROL ARMS?

Is it really a must do replacing the upper control arms when adding a 3" or 4" lift? I understand they are stronger but can you still get the camber/caster correct if you don't replace with the uniball upper control arms and just use the factory uppers? thanks

 

i had total chaos uca's on my previous truck and in addition to allowing the alignment to be returned to spec after a lift they also allowed about an inch more droop on each side.
if you choose not to use them you'll notice the factory uca's going from sitting relatively flat in the wheel well to very angled once the lift is installed. this angle basically puts your truck on its tippy toes and limits the suspensions downward travel.
bottom line... lifting 2-2.5 inches you'll get by without, lifting > 2.5 there is a good chance you need them and should consider it part of the cost of a proper lift.