the 3.4 is a 60 degree v6 similar to the 2.8 3.1 and 3.4 pushrod motor gm puts in everything except its got dohc heads and a rediclious cam drive system. it is however fairly stout. if you want to go boost your best option is a turbo. you can make quite a bit of power this way but if you want to go all out a swap is in order. you can swap it for a 3800 sc. the engine fits and about bolts in but will require a bit of a wiring nightmare.

as for people wondering why its a gtp but isint supercharged, the earlier gtp's had the 3.4 dohc engine the later ones had the 3800 psuhrod supercharged engine.