Just a couple more things. Since you have been in the auto repair industry for so long, it may be hard not to notice something that would otherwise be thought of as normal.
For instance, I'm pretty sure that the G6 features that same solid engine mounts found in the new 9-3, which has resulted in more felt vibrations from the inherently unbalanced Saab Turbo engines. There's absolutely nothing wrong with the engines, but the solid mounts which provide better chassis response to the engine will cause an increase in felt vibration. The PCM also holds the idle at the lowest point as well. When you shift into gear, you bring more mechanical parts into the equation which can reduce this felt vibration by spreading it out.
You will naturally get some fluctuation in idle, I was referring to it jumping from say 550 to 800 or more, and back. Just sitting, you're Tach should move just a little as the PCM constantly calibrates against the Idle Air table (I don't think we have an IAC motor since we have DBW).
Couple this fluctuation and change in Tone (Tone is the vibration) with an increased stiffness of the Chassis and engine mounts, and you're going to feel the engine more in the cockpit. I can think of few cars with "performance" tuned chassis and engine bays where you don't feel a "lope" in the cockpit.
Ever sit behind an LTX or LSX motor?