A turbine rotor blade with an aft flowing 5-pass serpentine flow cooling circuit in which a first metering hole connect a first root turn formed between the second and third legs to a core support cavity and a second metering hole connects the core support cavity to a second root turn formed between the fourth and fifth legs so that cooling air from the second leg can be discharged directly into the fifth leg while bypassing the third and fourth legs. A seal pin can be secured within the core support cavity to block the bypass cooling flow.