tank selector switch
 

ill startoff with sayin that i dont drive this truck but once a month or so, so when i do i usually only fill up one tank, the other day i decided to fill up both and while diving my front tank was about half full and figured id try the rear tank, when i switched it the fuel gauge didnt move it stayed at where my front tank was (half full), never stalled or anything, kept on goin, would this be a sensor in the tank thats shot or maybe a fuse? thanks.

check fuses