Forgive me if there is another answer for this question, but I haven't been able to figure out a good way to search for the problem.
On the iPhone5 simulator my background images are about a point short, despite being the proper size. See screenshot:

My images are all 640px × 1136px .png files, and my image code is below:
backgroundImage1 = [[UIImageView alloc] initWithFrame:frame];
[backgroundImage1 setContentMode:UIViewContentModeScaleAspectFill];
[backgroundImage1 setAutoresizingMask:UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth];
[self addSubview:backgroundImage1];
I would try it on my phone, but my certificate is expired, so I can't until the dev center comes back online.
Any ideas?