I start my car up this morning and my check gas light comes on, wife drove the car last. I go to gas station and put 6 gallons in it and gauge shows full. Not maxed to the peg like it usually is but full. After driving for 10 miles it's around 3/4 tank. I turn it off then back on, and it reads full again. I know it's not full. Any idea's ?

On another note, I got Suspension Techniques Sway Bars for Christmas and love them.