Why Is My Gas Mileage So Low?

1. Why is my fuel mileage so low in my Chevy Truck? 2. Why do all of my cylinders miss on my Subaru? 3. Why is my seat belt buckle so short on my Colorado? 4. How can I fix a coolant leak on a heater core of my Pontiac Torrent? 5. Buying a first car for my 16 year old help. 6. How can I fix a frost plug leak behind my Transmission of my Dodge van?