Shouldn't have to but you never know until you take the rear to full droop. Your 3" SL is it the articulator lift with revolver shackles? If not I doubt it but if you do have revolvers maybe. Every truck is different so until you install it and take the suspension to full droop you will not know.
Most times on the rear, and the rear is the one you would have to replace, you can unclip the OEM rear brake line in a few places and gain some length and still keep the OEM line. On mine I needed a rear line and changed the fronts to SS lines as well but that was really a matter of preference as I don't like rubber brake lines.
Mine at full droop with the extended SS line. Note that the shocks are disconnected so this is absolute max travel for the rear suspension.
The extended SS line seen at the right is long enough to still have a wee bit of slack. Also you will have to possibly unclip the ABS harness, shiny black line to the left of the brake line, to allow enough travel as well as extending the diff breather located on the left axle tube. If you extend the breather go ahead and do this mod at the same time.
Rear Diff Breather Extension
Install the lifts and see what needs to be replaced, moved, or modified. Anything that needs fixed will not stop you from street driving the truck. More than anything else go read the 2" BL lift thread again and make sure you have a list of everything that needs to be addressed when installing the lift.
READ THE ENTIRE THREAD!
