I too used to have the same problem, mostly with my other guitarists tone as he had a shite solid state vs my beastly XXX, totally agree with:
G0 T00BZ 0R G0 H0M3 !!!
In addition always set up your tones to it sounds best when EVERYONE in the band is playing. Fuck your own tone, its about THE BAND not you.
Although he's now upgraded to a tube amp and it's solved half our problems we were able to make a passable tone with the crap amp.
First ditch a load of bass (but not all) as your bassist will do all of the work for you and boost those motherlovin' mids!
as this is what guitars are after all. Definately reduce your gain as cranking the volume will help this out.... and clean = HEAVY!
I try not to max out my trebel so that it's not too thin or scratchy, but the other thing to consider which hasn't been mentioned yet is
the room.
You WILL need to re-eq your amp for every venue because obviously the sound will act differently in every room. On a very basic level and as a rule of thumb if you're playing in a massive room stick that bass back up a tiny bit maybe up one or 2 and also check how it sounds off of the stage (if you can - use your singer or something). For smaller rooms your tone can probably be a bit more like when you're jamming but just play around!
When you said it sounds awesome in the rehersal space when jamming and shit live it's probably because practise room is tiny - and usually moderately soundproofed if in a studio. Venues will most definately have fuckloads of nasty reflections bouncing around. So to answer your original question EQ is the issue here.
Out of interest what amps are you running through? Hope this helps you out!