They are not the same, but they are highly correlated
They are correlated in the sense that if you take the GRE once and only once it could be an indicator of ones IQ, I'll give you that. But the OP can prep for the GRE, buy the books, take practice tests, go through practice problems and section tests.... his score will greatly improve, hence the reality that the GRE is no longer of any indication of his IQ