"Well, in any case, the clock is ticking, and we have less time to rehearse than we would both prefer. I can play most of the pre-planned stuff just fine when I don't look at the tabs. Once I look at the paper, though, my timing goes out the window and my playing sounds like I've never even seen a guitar before... And that's not just with the pre-planned parts. It happens when I try learning songs on my own too... Maybe it's because the tabs make me think of notes as number of the frets and string, rather than intervals or actual sounds. Maybe it's not. I don't really care right now. I just need to know which notes to play and how the melody is supposed to sound."

When you try to read tab and play as you've learned, you're clogging your mind. Too many processes at the same time. Do you ever whistle or hum to leads? My guess is yes, can you whistle the lead to the song your learning when you cannot hear the music? If yes, you already know the lead, you just need to here it in your head as play the guitar like you do when you whistle.

axe2 posted a thread about scatting 3-4 weeks ago. Maybe after this next gig is in the books and you have more practice time add it to your schedule.

Just sing out some notes in rhythms or scales, then find and play them, helps ear training also. Maybe sing scales as you play them, get your mind to work with your guitar like it does with your whistle.

umm..... Hope you can whistle.