I was not clear in My post, nor did I know You were using pre heat and monitoring interpass temp.
If there has been fast enough cooling in the range from about 1500f down to about 800f to cause hardening, then the part should cool to about 150f before tempering so that all of the martinsite that is likely to form will have the chance to form, THEN You temper it.
If the preheat, interpass, post heat and slow cooling all work like they are supposed to, seperate additional tempering shouldn't be needed.