My dealer quoted me around $100 a couple weeks back, b/c I think mines going bad, too. Mine shows full after a fill up but then goes low much faster than the actual gas level does. It's happened for about 3 or 4 tanks now, and my mechanic buddy said it's likely the sender. Local parts store said it's a dealer only part, but $100 is better than I thought it would be. I'm waiting a while before I do mine. Using odo. If anyone can detail how easy/hard it is to replace I'd be interested.
Had to replace one before.
Wait until the tank is almost empty.
Remove the gas cap to vent pressure.
Put a jack under the tank with a piece of plywood between the jack pad and the tank.
Lift the jack until it supports the bottom of the tank.
Undo the straps from the inboard side of the tank.
Slowly lower the tank with the jack.
As the tank comes down you will get access to the tank supply, fuel line, return line, over flow, evap line, and electrical wiring. The hoses should all have clamps holding them on, remove all the clamps and mark the hoses and where your removing them from for reassembly, unhook the electrical plugs.
Once all lines and hoses are unhooked finish dropping the tank carfully.
Remove the tank from under the truck and clean all the dirt off the top.
There will be an access plate on the top of the tank this is the fuel pump and fuel level sensor, remove the screws holding it in. When removing the assembly be careful not to bend the float rod or you'll continue to get faulty fuel level readings.
Replace the sending unit then bolt everything back together in reverse order of disassembly.
Replace the seal/gasket on top of the tank, or you'll be removing it soon to correct fume or fuel leaks.
Make sure the rubber or plastic piece is on the bottom of the fuel pump, or you'll get vibrating noises and possible early pump failure.
Make sure you dont loose any excess pieces in the tank, i.e. gasket pieces, screws, or any other objects, they'll cause blockage and/or pump failure.
Be careful when unhooking fuel lines, even vents, they may contain pressure.
Start to finish is close to an hour.
Check trdparts4u.com for prices, if you not in a hurry to do the job they can possibly ship you the parts cheaper than you local dealer price.