Gas Guage malfunctioning

I have a 2002 Montana. Just yesterday, the gas guage started malfunctioning - reading full when I knew it was below half. It also jumps to empty and triggers the low gas warning light. Any ideas?

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very common for that era........gotten much better in last 4 yrs.........drain tank, remove tank, remove full pump/sender unit, replace fuel level sending card, assure proper oper, before installing, use new 'o' ring.............if MEGA miles on truck u might consider new pump at same time (a few hundred bucks)..............kjun
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