I've been told by folks who are in the know that the tranny will handle up to 500/500 HP/Torque.
Here's a link to the Vortech site for HEMI's. They only list the cars but I can't imagine they haven't figured out how to make this work in the trucks as well:
The Techo Supercharger system intrigues me. One of our supporting vendors here offers up a kit. Again, it's listed for the LX/LY car platforms but I'm sure they can put you in touch with the mfgr or help you with your application: