I recommend installing an in-line orifice of .050 in size. Few people have problems with vac gauges causing gremlins but the ones that do have pulled their damned hair out trying to find them. I discovered this the hard way and have cured another 4 or 5 cars of this mysterious vac leak by making and installing this orifice in their cars.
You wouldn't think a vac gauge would have that much effect but I imagine it depends a lot on how much demand you're putting on manifold vac.