Check your drive belts. My cousin has a sedan and he was getting bad mileage because the belts were almost gone.

I need to change my drive belts too. I see some cracks but I get 18mpg. Before I used to get 19mpg. That is for city driving. Highway I get 24mpg. I'm going to change the plugs and the belts and see what I get.

 

How do I know if my belts need to be changed?

 

Check to see if they have cracks in them or if they're missing chunks. You may want to check the tightness, too.

 

I have brand new belts LOL .. I've just resided to the fact that I bought a fairly expensive car, I drive way too fast and if I couldn't afford the gas I shouldn't have bought the car .. this way, when I get hit with $40 a week for gas it doesn't hurt as much lol I think infiniti purposely made the exhaust tone perfect between 3-4K so that we'll stay in that band and kill gas mileage maybe they have stocks in gas companies

 

I agree with the 4k note. I have an AT and I use manual shift. I shift at 3k and 4k when in 1st/2nd but I still get 17.5mpg minimum. You should be getting the same. You should start investigating to make sure your new block is good.