Go with the CST. The RCD moves the front tire out about an inch or so.... The RCD is a great kit but I think the CST is better. I have the CST on my 2500HD and I love it. Call Casey or Joe at Supertrucks in San Bernardino and tell them Donald sent you. They do great work. What motor do you have? You'll need to go to 4:56 gears if your going with 35's. My 2001 Yukon with 35's had to use 4:56 gears.
Good luck