I have a 2001 LS430 and the gas gauge is acting up.

When I fill up, the gauge appropriately shows full.

After about 28 miles, the gauge drops hard to just over half full.

It seems to move normally from there until the light comes on.

When I fill up, it takes about 15 Gallon.

Dealer has been unable to isolate the cause.

Any suggestions are appreciated.

Thanks,

Alan