You have the automatic E4OD? I've never driven an IDI with that transmission, though I have one on the floor of the shop that I need to sell. My experience with the C6 auto has been that a lot of power is wasted spinning the torque converter. With the T19, the throttle response is instant. My right foot is directly connected with the rear wheels.

The same may be true for swapping the E4OD for a mannual tranny, but with a locking torque converter, it may be less dramatic.
I'd swap in a ZF5, but I don't like (hate) automatics.
Heath