right now i have about 7 inches of lift and i just installed a slip yoke and cv driveshaft which has eliminated 99% of my drivetrain vibes so if your financials allow you i would recommend that but if not the t-case drop is a lot cheaper and will help alot. i had the t-case drop on my jeep when i had about 5 inches of lift and it cut down on alot of vibes. unless your original rough country kit came with extended brake lines, you are definately going to need extended stainless brake lines. your shocks should be fine for another 1.5 inches but i would recommend either new control arms or the RC control arm drop brackets. ive got the drop brackets on mine and they increased my ride quality by a pretty good amount. the only other thing i can really think about right now that you should really get is an adjustable trac bar.
if i were you i would DEFINATELY do the brake lines, t-case drop, and adjustable trac bar. ive been through most of this crap so if you need any other advise or ideas or anything your more that welcome to PM me