2003 Rail Pressure maxing out at idle

[Out Back 4x4]

I have bought a new rail pressure sensor, I am on my second dual cp3 controller, and have unhooked the belt and just ran bottom cp3. All of them max out rail pressure on start up. Is this a possible FCA problem or ECM? Is there any way I can test the FCA? Been almost two years on this build due to some stupidity on my part and a local shop, and I'm there, just have this hiccup.

Thanks for the help guys. I only have limited chances to get to the truck as it is at a shop about a half hour away and I'm working a lot. Will try your ideas and suggestions as soon as I can.