with a shackle flip in the rear, dropping the t-case is a good idea. it saves you from having to shim the rearend. i've done it to a truck with 8" lift and my blazer with 4" lift. in my case it stopped alot of rear end hop and vibration on the freeway. as far as negatives, sure you'll scrape at high center a bit more, but you just lifted it so add 6" plus tire say 35's so that's like 8"s total so 1" drop means at center you're 7" higher from the ground than where you started.