Fuel Gage Issue
 

My fuel gage on my 2000 Denali, has started to vibrate in position after the vehicle has been running about 10 or 15 minutes. The vibration is so fast that the needle looks twice as wide as it is. When driving the dampening of the needle is not always there anymore. If you turn the vehicle off then back to the on position the gage swings clockwise past the full mark to a hard stop point for about 5 or 10 seconds. It does seem to be reading about right. When you first start the vehicle cold, everthing seems fine for awhile. Any help would be appreciated. Thanks.