Aloha to everyone. My wife has a 1991 Cadillac Seville with the 4.9 L engine. It uses Premium gas and you know what that costs in Hawaii$$$$$. What can be done to help in the fuel millage as our top speed on the Island is only 50 MPH in a couple of areas. She loves the car and I would like to know what changes could be done to keep it running great and not use so much fuel. With a new computer and tune up in Seattle it gets about 12 to 15 GPM.