still having rail pressure issues

[Out Back 4x4]

I have replaced both FCAs, RP sensor, unplugged autometer rail pressure gauge, have truck hooked up to a snap on scanner, new dual cp3 controller, new injectors new top cp3, 30k miles on bottom cp3

Starts up fine but the rail pressure at idle fluctuates up and down 4000 psi like 4k to 8k 5k to 9k. Took smarty off and still same problem.