Yep, Taz nailed it. The Gen III PCM doesnt recognize the 58x reluctor unless you run a converter box (I only know of the one from LPE). The E40 is the odd one out, officially its a Gen IV ECM but only works with 24x reluctors. E38/39/67/etc are all 58x.

I dont know why GM made the change, imagine it has something to do with the newer ECMs having faster processors so they can actually take advantage of the higher resolution. Better emissions probably also plays a part somehow.