o2 sensor quits switching after fully warm

Guys,

I'm pulling my hair out here over a weird o2 sensor issue. I've switched sensors side to side and I get the same behavior over and over. This is in my 92 gmc with a 2002 5.3. The motor and computer came out of the stock truck. I am using a psi wiring harness.

When I first start the truck, I can watch both sensors switching as normal. Once the truck warms up to full operating temp, the bank two sensor quits switching and just sits around 450. As I said if I switch o2 sensors side to side I still get the issue on bank 2. I've checked the harness ground and voltage. I can see voltage from both o2 signal wires when the key is on.

Any thoughts would be helpful.