What year? They went from a real time gauge to an idiot gauge around 2007. Pinned on hi would tell me (instrument technician) bad sender or ground faulted wiring. I would go after the sender first.
04 SE, White, CC, 4x4, B.T., Pop w/capt's, Util. Bed package,Splash Guards,Floor Mats. No mods.(none planned except for inchannel vent visors and an 07 exhaust). Gas whore.