lately I've noticed that the needle on my fuel gauge drifts up and down while I'm driving (going up/down hills, braking, etc.) is this normal? Or is there a problem with the gauge/sending unit?

 

It's normal. The gas in the tank sloshes. The fuel sender is a float that rides up/down on a rod (like the float in your toilet). If your toilet was going up/down hills and braking hard, it would always be refilling with water (now there's an image!). It will always read fuller when car points downhill, and less full when car points uphill as well.