I recently installed a ported GT350 IM and I retained the IMRCs and factory GT throttle body. Because I kept the IMRCs and factory TB, I was able to drive the car after the IM install without a tune revision and the car idled and drove perfectly fine. A few days later, my tuner provided a tune revision for the manifold and I immediately noticed issues after loading the tune. At idle, the car would periodically stumble and the LTFTs showed that the car was lean at idle and during moderate acceleration. The tuner is claiming that there is a vacuum leak causing the lean condition. His explanation for the car running fine before the tune revision is that it?s running different cam timing on the GT350 IM tune that does not take well to vacuum leaks. Has anybody ever heard of cam timing exposing vacuum leaks? I'm currently using SCT to log so my log files are in csv format and too large to upload here. I can email logs to anybody willing to help. Thank you!