Fairly rocking song; the guitars sound ornery, and there are many things going on...
About the lack of highs: now, not to discredit any info you've gotten thus far, but in my limited experience (and maybe mix, Track Rat, or even Bruce could back this up)...
...don't boost things with EQ that aren't there already...
This has proven to me to make a decently recorded set of tracks sound wooly, and unclear. A good test is to solo a track, like the bass track, and boost the highs during playback... somewhere around 10k... hear that? Unpleasant, wasn't it?
Seems more important when seeking highs to 1) use a good mic 2) use a good pre/board 3) use proper micing technique 4) record in a nice sounding room
Yeah... these come before the actual "mixdown"... so it could be moot for you at this point. If it's impossible to retrack the drums and vox at this point... you could add a shaker track... or possibly a cymbals-only track, using a good clean signal path...
This song may have already reached the point where it's mixed as good as possible; i don't know... when mixing anything--salad, alcoholic drinks, tracks... you get what you put into it. EQ/FX aren't a magic wand... salad made with poor ingredients won't taste like it came from a 5 star restaurant if you just throw some ranch on it.
2¢