I just installed a rough country 2" leveling kit and 2" replacement rear blocks and 2856518 nitto terra graps. The transmission is hestitant to shift to 6th gear, even holding it at a steady speed on flat ground. It used to shift up un-noticed. Now I have to let off the gas or set the cruise control for it to get to 6th gear, and it doesnt always do it. What do I have to do to get this fixed???