I've been trying for a while to gain the motivation to slow down my favourite songs and learn them but I see myself having to slow them down far too much.

The type of music I want to play is Guns N' Roses, Alter Bridge, the stuff from Tremonti's solo album, etc etc etc.

This stuff is far too hard for me at the moment unless I was to slow all the stuff down and work my way up from about 20%, but I find it hard to motivate myself to do this.

I'd much rather learn songs which would challenge me and keep making me better and lead me onto playing the more difficult Alter Bridge stuff.

Could anybody recommend me some bands or guitar players who could lead me onto playing these kinds of songs? Rhythm and Lead.
Well, if you're having trouble being bored, that's just part of it. To learn difficult songs, you've gotta start slow and build your way up, it can get boring, but if it's what you want, it's worth the work.
Well, first, analyse your playing. Why can't you play these songs? What techniques are lacking, how long've you been playing and how often do you practice? Personally, from what I've heard of Alter Bridge, they aren't the most technical band out there, so I might even suggest looking at more difficult pieces and slowing them down so that you can learn the techniques needed to tackle some Alter Bridge. If you're serious about playing faster and tackling the speedier passages in songs, I could suggest slowing down some Yngwie Malmsteen, Sonata Arctica or Dream Theater, I think if a player focused a lot of their time and energy on playing some of their pieces at full speed, they'd quickly become good enough to tackle Alter Bridge without too much difficulty.

I'm a firm believer in pushing your limits, really, playing songs that are easier than the songs you want to play won't get you to where you want to be, however, playing songs that are harder than the songs you want to play will allow you to be beyond where you want to be now.

I will say, though, when you get to a certain level, you will need to slow pieces down, because there will always be something you can't do, and, if you're like me, you'll always want to do it, and slowing songs down allows you to perform them cleanly and with confidence. The motivation to practice needs to be there, the better you get at guitar, the slower you'll advance, or so it'll feel, I, personally, don't get any 'Eureka' moments, like I did in my first year of playing, everything I'm good at has come from dedicated practice, so, do be ready for that, and perhaps get in that mindset now, as it sounds like you may be approaching the point where you need to really take apart and practice pieces you want to play.