do I need to get a new fuel sensor ??
 

Just before I had been to ARCO and got its premium gas until to be full. Before the fueling I saw about 6 gas lights were on, but as a result I had to fill up more than 14 gallons.

A 370Z's fuel tank has 19-gallons max capacity, so it must mean that I had less than 5 gallons remained before the fueling. Then because it has total 16 lights to express fuel percentage, I believe I should have seen less than 4~5 lights turned on (19/16 = 1.1875 gal/one light), but actually mine was more than that.

Weeks ago my Z once did not recognize it had its fuel tank full after fueling, instead it showed only half filled up, so I just cleaned it with a fuel system cleaner and thought it was solved. But is it now time for me to get my fuel sensor changed .. ??

The 370Z fuel display is VERY non-linear. The answer to
lightsLit / lightsTotal * 19 gallons
doesn't give you an accurate indication of actual fuel volume.

just fill it up when u hit about 1/4 tank and no worries