That's very awkward. I would go back and retrace all the steps to installing your heatsink. As for the AS5 application, try this: put a small, bb-sized amount on the core and take a sandwich bag or something of that sort, put your hand in, and use your finger to spread it out. Once it's all evenly distributed, try putting it back on. Remember to not move the heatsink once it touched the CPU core because that might ruin the AS5 application and make it uneven. Remember to clean the CPU and HS really well with some acetone or 90%+ isopropyl alcohol. Don't use napkins or paper towels as they can leave little white dust thingys... instead, try using a soft cloth that doesn't have any lint.
The point of AS5 is to put as thin a layer as possible. It's just there to help transfer heat between the nooks and crannies of the heatsink base.
Another thing, YOUR HEATSINK SHOULD BE WARM. If your cpu temp is 50C+ and your heatsink is not that hot, it means that something is wrong. It means that heat is not transferring correctly from the CPU to the heatsink. I know you guys can say temperature monitors can be off, but if it was 45C w/ stock (which sounds about right) and 50C with the zalman which is proven to be a far superior heatsink, and in addition to that, the heatsink is not hot, it means that heat is not being transferred correctly.