Most of the mechanical things Pete list would have a noticable effect on the power of the car. If you have a high flow cat and the sound has not changed then its most likely not exhause back pressure. That leaves two things, Your system is lean and your system does not know it (O2 sensor) or your header are very thin walled and this glowing is normal. I have a very heavy set of of Stainless header on my 3.8 and they will glow. I only notice it at night but they glow a little with normal driving. I would imagine if I pushed the car i could get them to glow pretty good. The Stainless is now a nice gold color and that is with new O2 sensors.

 

Your headers just have "Rudolph envy". ;-)

 

Your car..it needs to lead santa so i can get my presents on time!! :O hurry! Google maps the north pole..youre running out of time..