I agree with the previous poster.
For alternative/pop/rock/metal/european shit, I always "AT LEAST" use six or eight guitar tracks done with diffrent guitars, picks, string gauge, amps, cabinets, pickups, amp settings, speakers, levels, mics, etc....you have to do this in order to get THICKNESS.
An SM58 is gonna go well to cut not more than half the guitar tracks you want, since it's a quite colorul mic. By this, I mean that even if you change amp settings or guitars, you wil still have the same "color" to the sound, which is a no-no in the thickness game. You have to get yourself two other mics, an LDC and an SDC and mix all those tracks to get the beefiest sound.
Also, crank the mids on both amps to the max, be easy on the treble and crank the presence up to the point were it's too much, then back it up a little...should give the tone a nice swirl in the high end.
And most importantly, turn the amps LOUD AS SHIT and use cabinets loaded with Vintage 30 speakers. For thrash, a 4x12 Mesa Recto Standard cab is hard to beat IMHO.