Many power boosts will give you either more power or better mpg depending on how you drive.
A good place to start is an induction kit or replacement air filter. A new exhaust can also help. Nige will quote you for a retune, see https://www.fiatforum.com/forum/topic.asp?TOPIC_ID=9458
An ecotek can also improve performance, mpg, etc. see www.ecotekplc.com