1. How old is your car? If it's an older model (but still fuel injected), it's time to see if the fuel injectors have become dirty. Cleaning the fuel injectors--especially if the vehicle has over 60,000 miles on it--does wonders for power and fuel economy.
2. See if the fuel filter needs to be replaced, especially if your car is more than three years old.
Fuel filter is easy... How do I clean the fuel injectors?
Is it true the on board computer will adjust for the octane? My van recommends 91 but some stations only have 89 or 93, others have 91. I use 89 if 91 is not available, but recently heard it is bad to go from one to another. Is that true?