37's with a fabtech 6" suspension?
 

07 fx4 with a fabtech 6" suspension....any clue if I could get KUMHO MT 37x13.50 on 20's to fit? Or possibly MickeyT MT 36x15.50 on 20's but it might be too wide?

If you add a leveling kit (standard Fabtech kit) or crank up the coilovers you could probably fit them with the right wheel, but it will be tight.

well i'm not getting the coilovers, instead going with bilstein 5100's for the front and rear....what about the 36x15.50? too wide? with 20x10 with 4.75bs?

Well, you need a 10 inch wide wheel with a 15.50 inch wide tire. I'd rather have at least 5 inches of bs, but that may work. It will be tight because the tire is so wide.