If you have 12psi on a 3.4", then you need more flow mods.

To add, you're on a stock valvetrain with an LS1 TB...why? Not needed.

Also, catback is worthless as well...giving you no power gains.

Injectors are not needed either, stockers flow fine down to a 3.1"~.

I'd do more research before looking further into mods if you're asking about Edelbrock heads for a SeriesII 3800.