1997 Dodge Caravan 1997 caravan burning to much gas

hi guys, i have a problem with my gas milage, it seems that i am doing about 8 mpg, i noticed this after my fuel pump and tank was replaced. i was just wondering if it could be something like theres no pressure in my tank or air getting inside or maybe a vacuum leak somewhere, any advice would be good, if someone can just point out some thing for me to check or do would be nice

thanks