(which I know is somewhat normal)
Probably not. None of what you describe sounds in any way normal, but well, you have not provided any useful info. We know nothing about your project, your comp settings, effects used, footage involved, MP settings and whatever. We do not even know what version of AE nor any proper system info. MacBook Pro? Yeah, which one then? Which version of OSX? You need to be moch more precise and provide much more info instead of losing yourself in vagueries and generalized, for the most part probably unfounded and wrong, assumptions about AE misbehaving...
Mylenium