I am running an 03 Denali with 408 with a 1900 on top. We made 727 hp and averaged 650 ft/lbs at the flywheel. I built the tranny with everything including billet shaft and it is holding fine. The denali is built well except for the tranny. I basically agree with Zippy on all his suggestions. I went with the 1900 because the 2300 wasn't out yet, still we are making huge power on the 1900 with only 6lbs of boost but I am running quite a bit more cam with some ported heads and other fun stuff. If you dont want 600hp at the wheels you can always run the 1900 but for the extra I would go big.

 

Thanks. I don't remember the level7 as an option when I got the FLT5.
I will think on it a while but the TVS 2300 makes more sense unless the 1900 goes on fire sale or someone has the kit and now wants to upgrade.