2008 Nissan Maxima hello

i have a 2008 nissan maxima se i have been having 3 problems for awhile now. one is my gas gauge does not work right, it shows less then what i really have in my tank and i know for a fact my car is better on gas. Second my low tire pressure light is always on, even after i got new tires put on not too long ago it still is always on. Last my display screen flashes on and off. I would like to know what could be causing these problems and what needs to be done for it to be fixed? Thanks!