Toyota Repair: Toyota Previa Fuel Consumption, firestone firehawk, gas mileage

Question
Happy New Year Ted,

I have a supercharged Toyota Previa DX that is about 8 years old with 34,200 miles on it. It is a model 5124A Previa.

I have been calculating my fuel consumption and for city driving, I get about 14-15mpg and for highway driving, I get about 16-18mpg. When I came back from a snowboarding trip from Lake Tahoe, I got about 20mpg. The specs for the Previa call for 18mpg for city driving and 22mpg for highway driving.

I checked my fluids and they are good and at their proper levels. The air filter was changed at about 28,000 miles. The spark plugs and spark plug wires were changed at about 31,000 miles. I also check and maintain my tire pressure at 35psi.

Also, the Previa got into an accident and does not seem to be properly repaired because the driver side door seems improperly aligned, could this be a factor?

Could it be the new Firestone Firehawk SH30 tires that I purchased?

Could it be how much I load into the Previa?

Could it be the hills that we have in San Francisco, CA? I know it could be a list of factors, but please at least tell me what I can do to alleviate this problem.  

Answer
The tires have very little to do with it unless they are way underinflated, make sure there is at least 34psi in the tires which sounds like you have been doing, the other factor you may consider is the load factor that you have mentioned, increasing vehicle cargo load can greatly decrease gas mileage, the door alignment definetely is not a factor.
I don't believe it is a fuel management problem with the EFI system because if there was the check engine light would come on.