You definitely have a vacuum leak with 10" of vacuum at idle. I have seen cases where the lower intake manifold gaskets have slipped out of place. This creates a vacuum leak in the lifter valley that is almost undetectable by most normal means.
Check up the fuel injector seals when you replace the gaskets. If the injector plastic pintle cap is missing, the O ring can slide down into the intake manifold.
My favorite trick that saves time and effort is the stay in place gasket. Be sure that you scrape (don't use a wire brush) all the old gasket material off, then clean all the surfaces with acetone or MEK.
When the surfaces are clean, use weather strip adhesive on the head to manifold surface, and on the side of the gasket that mates to the head. Follow the instructions on the tube or can and when it gets tacky, press the gasket down on the head.
Clean the area where the rubber rails mount to the block in front and in the rear with more acetone or MEK and do the same trick with the weather strip adhesive that you did to the heads.
Coat the rubber seals and the gasket area around the water passages with lots of Blue Silicone gasket sealer and put it together. Yea! no leaks, and no gaskets that shifted out of place.
If you reuse the injectors from your old setup, a repair kit is available from most auto parts stores if needed. Coat the injector body "O" rings with oil before you use them and everything will slide back together. Take the other advice you got here and run with it.
Fuel injector seal kits with 2 O rings and a pintle cap (Borg-Warner P/N 274081) are available at Pep Boys auto parts. Cost is about $2.74 per kit. The following are listed at the Borg-Warner site (
http://www.borg-warner.com ) as being resellers of Borg-Warner parts:
http://www.partsplus.com/ or
http://www.autovalue.com/ or
http://www.pepboys.com/ or
http://www.federatedautoparts.com/
Most of the links above have store locators for find a store in your area.