I have a 1998 GMC Jimmy (4.3, 4WD). It has 115k miles and was a one owner vehicle. I've owned it about a month. Previous owner changed oil every 3k miles. I just changed plugs (platinum), wires, rotor and cap. The vehicle is not throwing any codes. I drive about 3 miles one way, twice a day. I'm getting about 10 MPG (or less). My previous vehicle (1994 GMC Sonoma, 4.3 TBI, 110k miles) was getting about 15 MPG in town. I was lead to believe that the multi-port injected, better balanced motor in the Jimmy would get better MPG. What gives?