Thanks, rickisrad.
Never done an intake before. I believe I've installed this one correctly, however, since I'm not experiencing any coolant or oil loss, or observing any leaking.
The vehicle idles normally.
Used plastic gaskets from Autozone.
I reused the plastic plenum. I didn't observe any damage, including melting around the EGR tube. It appeared to be in good shape, so I reused it.
I was also careful to follow the torque sequence and specifications of GM for my Grand Prix GT.
I'd been warned about installing the thermostat correctly; I made sure to do so.
I really appreciate your response and detailed questions, rickisrad.
I've actually resolved the issue elsewhere. #1, I remembered that this car had been overheating before I changed the gaskets. #2, I found out that it actually isn't overheating at all. A mechanic measured the temperature of the thermostat housing itself with a digital point 'n read thermometer, and another mechanic read a normal temperature of 201 F from the PCM while the gauge read 230 F.
So I'll need to replace the gauge cluster. Any ideas for a cheap replacement cluster?