Usually when running I can see the needle on my gas gauge moving as the fuel sloshes in the tank. The past two trips it has been pegged at 3/4 even with less gas in the tank. Being that when I turn the Key off, the needle drops I am guessing my problem is in the sending unit. I reached up under the dash wiggling wires and that didnt do it. How would I test the sending unit? where would I get a new one?