Originally Posted by MixManSC

Only way you will be able to determine if it has a non-original tune/flash on the ECM will be to use a higher end tuner like EFI Live, HP Tuners, or a GM Tech2.

One way to check for intake leaks is to remove the upper beauty cover from the engine, start it up and let it idle, then spray around the edges of the intake, throttle body, injectors, fuel pressure regulator, PCV tube, etc and if the idle changes in a spot, there is a leak. Do this when the engine is cold and do NOT get any spray on the exhaust manifold. You can use a can of carb cleaner or even a propane torch (NOT lit obviously I hope). Do this outside and good idea to have a fire extinguisher handy. A fire is unlikely but better to be safe.

These mention what I'm talkign about. I've done it a dozen times myself....
https://www.jalopyjournal.com/forum/...sting.1032664/

One of the issues on our engines (and all GM LS engines) with the plastic intake manifold is the intake manifold gaskets can harden and deform causing small intake leaks.