Slow parts can be a pain - there's just so much room around each note, and rushing a single note by a few ms can ruin the whole thing.
One silly thing that helps me keep the feeling and to let go and be less mechanical is to actually record a dummy guitar track if possible. I've noticed early on that if I had to record similar parts hard panned left and right, I struggled w/ the first one and the second one was much better, so I stopped wasting time trying to record THE right take the first time. I just go back once the second guitar has been recorded and re-do the first one.
Another things which used to slow me down a lot is that even though I use amp sims - I insist on re-recording everything the minute I change something like a cab or if I add distortion - because I'll react and play differently.
To be honest, I think the main reason why I have a tendency to pile up tracks is not mistakes, but sounds. And each new sound means doing a bunch of takes.
Archiving the old sounds and creating new tracks all the time isn't an efficient option either as I'd end up w/ tons of tracks and plug-ins to manage. And it's always tempting to re-open the amp sim and modify the cab or add a little this and that.
One thing that helps w/ that is that my host has input tracks, so the sounds are "printed to tape" as is. I'll usually record a few different options and pick what seems to work best afterwards. There's something about committing to a sound and making it work.
And then of course, spending time away from it. I'm sure I've deleted more than my share of good performances because I just kept at it too long. A producer will make that call for you. When I think back about the time we spent in a real studio - man, we rarely did more than 2 or 3 takes, and I was pretty happy w/ the results.