2002 Dodge Intrepid Code P 0440

I pulled this code up on my own doing my own diagnostic test, P 0440. I looked it up and it says the evap purge system, I am a female and I am at my wits end of trying to figure out what this means, My car was in the transmission shop, a nationwide one, they kept doing guesswork on my car replaced everything in the transmission when it didnt need it, I had to go to Autozone to find out that it was the transmission moducle inside the computer instead of the transmission. This had been going on for 2 years. At any rate I just got my car back and its using outlandish gas amount. I have looked til im blue in the face. But since the transmission shop dropped a motor mount they busted a fuel line, ok that was repaired, this code that comes up on the dash will this evap purge system fault fix what is going on with my gas mileage, before this shop I was getting 450 to 500 miles easily, Please if you have any ideas if let me know, im at my wits end. The car drives perfectly fine except for the gas mileage and with gas as high as it is, has come quite expensive. Any suggestions