i put fuel in my truck and filled it up and the gauge went all the way to full then at the end of the week it still said full but i know that wasnt true. then it started bouncing up and down then when i stopped and it showed how much i had which wasnt much so i filled up and its still on full is there maybe a ground lose somewhere or why else would this happen?

 

Sending unit can be faulty as well or the connection or float can be stuck?

 

it could be all of those