1. If you're on the highway it is more efficient to use the A/C. If you're in town under 45mph, roll down the windows. The A/C is belt driven so it saps power from the engine. Stop and go traffic with the A/C on will kill your mpg.
2. I have never had this issue. My tank fills up completely every time.
3. The shift lights are designed for maximum efficiency. Rule of thumb - Shift at 2k RPM.
4. If opening and closing all of the doors does not fix it, you may need a dealership visit.
2011 SES 5spd #006 >> SR #213
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