Hi Eddie - I too use an SM58. My mic interface is an older Tascam 8 tk Portastudio 488. I record with the EQ flat.
I also make sure that I stay 6 in. away from the mic. The SM58 has a great proximity effect for live singing, but can be over-powering on the low end for recording. So if you keep back from the mic (behind a pop filter helps) you can save yourself some EQing hassles on the low end, and then as Scott suggests, use a highpass filter for light tweaking on the low end.
At least that's how I've learned to handle the 58 on my system. Sometimes I use a nano compresser set at 2 or 3:1 because my voice can be spikey trying to hit high notes, or too soft trying to hit low. But generally no applications of anything until after a clean record.

Cheers - Ian

Ian
My "Original Tunes" Site
My gene pool needs more chlorine.