It is possible but will not be very cheap. You my be out of luck on upgrading the 3.4 but your trans is the same as in the grand prix which has a pretty good aftermarket. You would want to start with a 4t65e-HD out of a GTP (yours is the standard 4t65e). You will need to have the PCM tuned as the gearing is different. I know a few of the GTP guys are running some serous power through the HD trans but they are beefed up. I would look at
www.3800performance.com and
www.zzperformance.com and tell them what you are wanting to do and they can point you in the right direction.