Two things I've learned--
First of all, when you are memorizing in the way I believe you are, via muscle memory, you are setting yourself up for failure if your memorization is done any time less than 8 weeks out. That's about what nerves does--it you play your piece like it was eight weeks before the performance. Ideal? I think not. Believe me, I've learned how this can go wrong, the hard way.
The second thing is a solution to the first. Memorize in sections--phrase by phrase, measure by measure. I'm even experimenting with memorizing as I first learn a piece, rather than learning it by sight, then memorizing later. I haven't tried this out personally, but I feel like having a piece of music intellectually committed to memory, as well as in muscle memory, is far stronger than performing by muscle memory alone. I'm getting ready to a concerto competition, so we'll see how well this method goes ...