I guess I noticed when I was not 'down pat' on knowing a song such as new one aded to the set, I felt all kinds of nerves about it and over-thought it. It's like the first key to making errors.
I remember adding BTO's 'Takin' Care of Business' to the set. Not a complex song by any means. However, there is a good handful of fills and solo material in the tune. The rhythm was easy but it was really just a matter of days from when everyone (but me) chose to add the song to the set to when we were going to gig with the song. I pretty much learned the solo stuff but didn't have time to practice it and ingrain it in to my skull...I remember going in to the song during the few practices and then the gig just thinking 'Man, I hope I don't....' Well, you know...the alternate version of 'screw up'.
I did, royally.
I could play 'Crazy Train' fills and solos or Dokken's 'When Heaven Comes Down' without batting an eye but I had them down cold. No nerves when playing them and that made it fun. That stupid BTO song killed me (until, eventually, I had time to actually practice it.
So, the point...I wonder if, even though you practiced the stuff, do you feel you have the 'I can do it in my sleep' familiarity for the songs. Or even more to the point; you might actually have them down but do you feel that way?