When I first got mine it would do that a lot. Say once every twenty times. I replaced the terminals on the battery and it stopped. For a while. It has started doing it again, basically I try and start it a bunch of times really quick and it will astart cranking again. I'm beginning to think it will be the brushes in the starter myself.

89 SWB, V-6 5SPD, OME Shocks, 16.5X37's, 2"BL, SR axle, Gen2 brakes, Lincoln w/Superwinch