Do you have money for another motor? The 3.4 has claimed more engines than any other pulley. You are running a stock tune, a restrictive exhaust, no valvetrain mods, and a smaller pulley? And you ask how do I know you have KR? Not trying to flame you- just stating the obvious.
Another thing, how did you chop off your resonator? did you weld a straight piece of pipe in its place? If you did, then you could do the same for the U-bend. And buy a bung from Mcmaster (about $2.00) and weld it in the pipe for the O2 sensor.
That is what I was wondering. If you are running a 3.4", I bet my neighbor with a bone stock GTP would beat ya. Likewise...put a stock pulley back on that thing. Your car will thank you. 3.4" pulley most of the time requires something like @ LEAST, intake, 180* T-Stat, DP/U-Bend Delete/Headers, Tuned PCM, Colder Plugs.
If you want to spend a few bucks on it and can weld it in yourself, here's a u-bend delete.
ZZ Performance
I would also check with your local exhaust shop and see how much they would caharge to do it. May come out cheaper.
the front exhuast manifold IS very restrictive. the whole manifold set up period is restrictive. yea after that its all fine.
and if your running a 3.4 and getting KR, then that pulls timing and thus making you slower.