I just went through this. Since I've owned my plane, the vacuum gage has never been above 4.3 to 4.5 inches. Even after adjusting the regulator to max. This summer I had the shop put in a new gage. During the ground check, the vacuum was so high that it broke the needle off the gage.
The high vacuum probably tanked a new [exchanged, overhauled] DG that was put in 18 months ago. Cost another $380 to overhaul it again.
My point, make sure it not a vacuum gage problem.