Cat and Exhaust Pipe Glowing RED

Here I go. I have a 2004 RX8 with 81K it is all stock. A week ago I noticed the cat was glowing red after a 15 min run on the highway. I stopped and started to do some research on here and I changed the Coils, Wires, Plugs, High flow Cat, and the down stream O2 sensor since I got CEL. I did all of this the same day. I also had Mazda checked compression and it passed. Last night when I got home I decided to check underneath my car and what a surprise, the end of the cat and pipe was glowing red again. I tried researching before i posted here but came out empty. Can someone help me..?

Cat and Exhaust Pipe Glowing RED