My GMC Jimmy waste huge amounts of gas. I dont believe I even get to 8 miles per gallon. It has 160,000 miles on it. When I stop at a light and then press on the gas I hear a gargling sound as if the gas tank had air in it. I've been told I need a new gas tank and I want to make sure that that will fix the problem. Also, my gas reader shoots up and down and its never accurate. Could this be related to the gas tank problem? Thank you in advance. I would greatly appreciate your help.