Code P0436 and gas gauge floats

[Cornel]

I have a 2006 Envoy Denali and the check engine light can on with code P0436 also my gas gauge will go from 1/2 tank to empty and then back to 1/2 tank or what ever gas is in the tank.. Are these related problem and Does anyone know what I need to do to correct?
Thanks
Cornel

 

[Cornel]

The highlevel fuel sensor was the cause of my fuel gauge dropping to "E" and then going back to correct gas level.. Basically what the P0436 code says needed to be replaced.
this is a $500 part