So wtf is going on with my fuel gauge?
Is it possessed?

For instance, I was coming home last night. Now, I know I have a 1/4 of a tank. Yet when I get in it shows a FULL TANK! I'm like SWEET, but i know its not really full. So after driving a while, it slowly but surely falls back down to 1/4 of a tank. But that took like 20mins of driving to do that.
Another time, I was sitting in the parking lot at work listening to some music before my shift. So, I turn the A/C on cuz it was freakin 85degrees outside. So the radio is playing, A/C is running, and I look down and my Fuel Gauge is dancing to the music. So I'm like, WTF? Just jumping from empty to fuel and then hang out in the middle a little while. I watched this for about 5min and then cut it off and went inside for work.

So is it just a bad sensor? Or do I need to replace the whole gauge cluster.
Or is my fuel pressure surging and falling?
Also, this problem may be connected when I turn my A/C on. I have noticed that it does it more when I turn it on.