2004 Nissan 350Z Car Stalling

I had some work done to the engine of my 2004 350z. Major changes such as pulleys, cams, higher compression and such were introduced. The problem I've experienced since the change -- The idle speed needed to be bumped to 950 vise the 650 it was previsouly set too, thinking that by reflashing the ECU would fix the stalling of the vehicle coming into a stop from driving at a range of 3-4k RPMS. The engine stalls. Few friends think it could be the pulley system not delivering the power needed too keep it running idle, the Oxygen Sensors not working properly(I have the generic universal ones). I had the spark plugs replaced with Iridium, still to no avail. I'm still having the Same issues. If you have any further expert advise on the matter, I would greatly appreciate it. I've uses many resourses and avenues to try and correct the problem.