I had the same problem but I had a bad lpop
If it isn't getting EOT it'll default to like 175 degrees or something.
The LPOP only has around 70K on it and I bought a high dollar Melling when my buddy did the overhaul.
The issue turned out to be the IPR. It was bad. I just swapped that one in when I was having a different issue which turned out to be the P/U tube in the rear tank. I took that IPR apart, cleaned it up, and swapped it in when I was diagnosing it. I didn't change the O rings. I just took it apart to clean it.
So I was ignoring it because it was freshly cleaned within the last 8 or nine months. Turns out it went bad. I bought an O ring kit for my spare here locally. The truck is running like a sewing machine now.
Thanks again for your help!