And it doesn't take long to become a shredhead , you just fall in love with something and try to play it ... I'm usualy not in a rush , I have other things to do in life , so when I decide to play some realy tough solo , I learn it lick by lick, taking only one small lick a day , probably I practice it for a couple of more days to completely master it before going into the next one.
The best thing , after you learn a couple of realy tough pieces , normal stuff becomes a lot easier ... If you're a new memeber in a band that's going to cover some not played often metallica tunes and stuff that you haven't played before or have forgotten , you'll find yourself like learning a whole set by an overnight .
One thing I learned from my humble experience , push yourself beyond that thing you want to do ... Say you're gonna perform "Far Beyond the Sun" as a guitar solo break in the middle of a gig , you should try it at home with faster tempo even if you mess up a little , so that you can easily play it up to the right tempo without messing too much live.