Can we see a picture of the offending tool. Is it possible that the tool is heating up the plastic then when the part cools the dimensions are wrong. This is something i've seen with alot of plastics but its been years since i've messed with glass filled phenolic. I do know that the tool is not shrinking during the cut. Also runout issues would cause enlarged cavities not undersized. Best bet is to go with the tools that you know work.