Ok, maybe its because I'm getting a little older and mellowing with age, but I hear your question, or rather you request for a "challenge" in a bit of a different way. If its just hot licks you want, then just ignore the rest of what I'm saying - that's cool.
But listening to what you tell us you're playing now and hearing the suggestions others are making to you I think you should challenge yourself to play something peaceful and packed with emotion rather than trying to get more and more sizzling licks to scream from your finger tips.
Many great rock artists have done this with sometimes astounding results. One that comes to mind is "Beth" by Kiss. Another interesting approach might be to play something like Whiskey in The Jar, like Metallica did, but go find the Evans & Doherty, or other Irish musician's more original version and master that - Gaelic lyrics and all - then switch it into the Metallica style and see if knowing where the tune came from makes any difference to how you feel about where it is now.
You could be surprised at how diversifying your talents and understanding of music will effect the way you play. Try not to forget that it isn't always about the destination - sometimes the journey itself is where the real joy is.
However you find new challenges, I wish you all the best!
