Have you considered shaving your differentials, relocating your shock mounts, and just cleaning up the undercarriage in general? Much cheaper than bigger tires, and will still benefit you when you do move up in tire size.
I am not too familiar with the super duty diffs, as my 2005 f350 v10 with a Dana 80 & 60 is new to me, but this is a very popular mod for older Chevys with the 14 bolt.