Just bought a 1971 GS Stage 1 hardtop drove the 500 miles home over 2 days. Trans changes up seamlessly on medium throttle, but once in top gear wont kick down when I floor it...the engine just pings!, got forged pistons so itll handle it but its not good. Rang a mechanic mate who reckons these cars have an electric kickdown switch? any ideas?...dont wanna burn up the trans! Starting out in Low itll lay 2 strips of rubber till I manually shift to second, gears are on the column but. Gonna be on the dragstrip on the 21st of this month so Id like to have everything tip top by then. Help!