Put your truck in entry/exit mod and then measure to the tip of your antenna.
I've got 6'5'' on mine to the FM and 6'3'' to the Sat....so I would have no issue driving into a 6'5'' or better.
I would also be willing to chance a 6'4'' depending on how hard my antenna hits when I go under the height check and how steep the ramp breakovers are
