Just a couple of simple things because I'm not really qualified to get too technical with it all. First, from what I understand Slash was a lot like Jimmy Page in the way he approached learning guitar, in that the both got their "chops" from listening to other guitarists, and learning their songs and solos. You might want to research the players that influenced Slash, and learn some of their songs. Don't pick stuff that is super hard and technical to figure out... its the ideas you're after, not necessarily the speed and technical difficulty. You're looking to get a bunch of licks under your belt that you can then intuitively draw from when you go to write a solo of your own.
With that in mind, I don't think Slash probably thinks too technically about a lot of the solos he plays. Its probably a lot more just gut instinct, which he cultivated by listening to a lot of other musicians who played stuff he liked, and he's consciously or sub-conciously borrowing from them.
One thing you could try is just humming or singing along with a backing track instead of trying to play a solo right away. See if you can sing the solo, then work it out on guitar once you have a solid idea of what it is you want to play. This way you can come up with creative melodies without having to worry about what the notes are or what scale you're using. You can use your theory knowledge to guide you once you've already come up with an idea of what it is you want to play.
Just a thought...