Have you measured the lift at the retainers at max lift between the other ones versus the one you're having issues with? If not you should up,
I have found more than one rocker arm that wasn't the proper ratio puke rant
The other thing could be that lobe is not ground exactly like all the other lobes on that cam on the base circle, heel, of the that lobe scope twocents

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)