there is not a button...
on the drivers side of the shifter ? i know everytime i stick my hand in the cubby hole under the temp control i always turn on the perf shift . check your owners manual they may have done away with it, that would suck but since buick moved up in gm's car line adn took caddys place in the line up, buick is goin to be like the caddy was classy not fast, pontiac is driving exict, cady moved up to comp with BMW and all them.