Don't forget that TT can also represent a "tummy tuck", which the reader can usually figure out from the context of the discussion. For the OP (original poster), a TT (tummy tuck) is the installation of a high(er) clearance transfer case skid. These raise the transfer case up higher, and effectively create more ground clearance under that area of the vehicle. Just know that to do this can potentially cause driveline vibrations and clearance issues between the transfer case and the floor/tranny hump. So here's the common formula to do it properly: TT, BL, SYE, MML, and adjustable rear CAs (control arms). Simple, no?