or maybe somthins wrong with it, but anyway every time i fill my car it either overfills and gas spills all over the place or like what happened today it under filled it stopped at 40 bucks thats where it sopped like it was full, i get back into the car and drive away it only filled it up to 3/4... 9 times out of 10 it doesn't stop telling me its full like at all it just over fills... does this happen to any of you? (please be easy in the replies...im still a newbie i dont know much about chevys) thanks for your help

 

rusted tank ? your overflow is disconnected or loose? or your filler hose is loose

 

I dont think you have any holes in the tank or loose fittings or you would probably notice the huge expensive puddle under your truck. I would climb underneath and see if the vent hose is crimped or obstructed in some way. If youre not sure what to look for, Find someone with the same year truck (Also 2-door vs 4-door). Explain the issue and see if you could look under theirs to compare.