I got this 06 Monte Carlo LT with 145,000 miles well maintained and I’m looking to tune the 3.5L LZE motor for more power. My friend had a tuned 3.5 Monte with 300 hp yet he don’t know where it was tuned. Can anyone shed some light on where can I tune a 3.5? I’m in the Chicago area if that matters

 

You might have to look into local performance shops to see if they do it. The one guy that I knew that tuned the 3500, has left the w-body scene and no longer does tunes on these engines.