I have a Sedona, LX 2002 3.5 liter V6 engine. Dese days m noticing a drastic change in my fuel economy. All I get is a 30 mpg. Since I keep the AC and stereo switched on most of the time, I thought this was the main reason. Is it so…?? And also suggest me some upgrades for my car that I can add to make its performance better and efficient.