grand am gauge cluster problems and engine trouble

I am having a problem with the entire gauge cluster on my car. First the fuel gauge. Whenever i fill the tank it goes way past the full line and it takes awhile for it to even go down. The voltage meter reads lower and lower with accesories turned on such as lights, fog lights and especially rear defrost. I've had the voltage problem check and the battery and alternator work perfect. The blinker works very slow most of the time and even slower with accesories on, lights dim and brighten with each little click, also tachometer moves a little while the blinker is on. After car has been running for a good 15 minutes or more, the engine oil pressure gauge starts to drop, about 20 when idling and about 45 when moving. Engine temperature gauge seems to work fine, goes up as the car is running longer but never has never reached very high. air bag light is always but I don't know if it's supposed to be on or not. When the voltage meter would drop I could just be sitting there and rev the engine without it moving and the mph gauge would go up with the tachometer, and while accelerating it would hit 80 while i might have been doing 40. Occasinally the service engine soon light comes on after being first started for awhile and stays on after driving for a few minutes and it goes off and doesn't come back on again.

Now for my other problem. It has normally happened when I first start it in the morning and just go rather than wait a couple minutes and it did this when I first bought it. What happens is the engines rpm's go down to about 500 and the car just about cuts out and it revs itself up to about 2000 and drops and the revs again. Sometimes it stays at 2000 and if fine within a couple minutes. It has done this to me while going through an intersection and it just made it to the other side of the road, but I had to sit there with my hazards on for a few minutes. Gas pedal is also unresponsive when this happens.

Any questions, feel free to ask. And any solutions to the problems are greatly appreciated.

welcome to the forum. In reference to your jumping RPM issue, my bet is that it is either a bad MAF or a bad TPS. Replacing both should solve the problem.