Use a better gauge, a wider one that can show you in actual 2 psi increments rather than this tiny item. The little fluctuation you see at idle is your fuel pressure damper not working right - due to the missing volume.
And this was not a full load test as you claim - a full load test can only be done when the car is on the road in a lower gear and you are at full throttle from 40% engine rpm range all the way to redline.