Boost surging between 11-13psi, Boost set at the 13psi with boost controller but falling back Options

[cax_11]

I got a go fast bits boost controller, set at 13psi, at full acceleration it goes up to 13psi but the falls and rises back to 13psi rapidly, I can feel the acceleration jumping and falling back accordingly, Spikestop is off on the boost controller, and when I turn off the controller and run wastegate 10psi it doesn't jump around at all, what could cause this? On a cold night it tends to be better behaved.