Ummm... I think you need to free up your mind... and, er, fingers... (ma-an) :lol:
You're already playing lead live - and getting away with it? You've learnt a bunch of phrases and licks, enough of them so you can string together a solo and fool most people in the audience... but you don't feel like you're fooling yourself enough anymore?
What I found, to get past that blockage, was obviously some sort of "mind freeing" - but I'm blowed if I can figure out exactly how I did it. I'm still playing the same licks and phrases, but nowadays I feel like I'm talking with the thing.
If you've got another instrument lying around that appeals to you - put some time into it, it helps the guitar playing in some mystical hippyish way. I played bass in a worship band for a few years, and I taught myself to play piano so I could write more freely – both times really improved my guitar playing without me practicing guitar at all!!
Theory is not a bad thing - but don't take the stuff too seriously :lol: Don't feel you have to learn it - just know about it. I know about modes etc, and I know roughly which page on which book on which bookshelf I could find some - but I don't know the intervals for each mode, I couldn't play you one.
But I do know an AWFUL lot about harmony and how chords are constructed and what intervals are used to convey certain moods emotions, and how the melody and bass line change the chord that we guitarists think is the one we're all playing.
I'm also a dab hand at finding new ways of playing simple chords somewhere else on the neck so it sounds interesting - sounds like you might be as well? If so, start thinking about this - scales and melodies are just chords strung out, and chords are just scales all played at once.
I originally started playing lead years ago by thinking "the chord is A, so I know I can play an A, an E, and a C#, anywhere on the neck, I guess as long as I don't stick around too long on the inbetween notes, I can also play any linking note that's in the key the song is in..." – I actually walked on stage with that knowledge alone!! (what an arrogant git I must have been :lol:)
After that I started learning Black Sabbath, Deep Purple, Led Zeppelin, riffs - never solos, funnily enough - and then we discovered Chuck Berry licks, that sort of thing. And someone introduced me to pentatonic scales, and I picked up my own way of doing it which is pretty much a dorian mode with something else chucked in... And I stole what I could from where I could... But I've never really lost that "the chord is A, so I know I can play an A, an E, and a C#, anywhere on the neck..." approach.
What I'm saying is, if you're good at chords and harmony - use that knowledge to expand where you're allowed to wander on the fretboard when you play lead.
Lastly, make recordings - by all means jam along to backing tracks, that gives good sub-conscious work outs and relaxes you, and if you make a mistake that sounds good you've suddenly got a new phrase/lick/trick in your library... BUT what I've found really stretches me is RECORDING IT. Especially, trying to record a song where I've deliberately planned "NO Solo", but there's say 6 bars when there's no vocal and something interesting has to happen, and I happen to be a guitarist... so up steps "Mr Axe hero" for his lead-break, and at first I can't think of anything worth saying, but 5 hours and 100 takes later something evolves out of all the cliches and mistakes you chuck at it... you have that perfect little "guitar bit" that on commercial records sounds so spontaneous and original (but of course it's neither).
I think it's related to the hum a tune and try to play it suggestion, but you put yourself under pressure deliberately because you've only got 6 bars to show yourself how good you are, and - because you record it - you can judge, and you can't get away till it's done. Try it- you'll be amazed what you can come up with. Do this a few times, and you'll suddenly find one day that you can break free of the licks and phrases, if only a few moments maybe - but just enough to make it feel like you're talking when you're playing...
I do hope there was something useful in all that waffle! :D