I have 264/272 cams and my boost guage reads 10 Hg at idles (not even sure if that is where it should be??) and when I let off the throttle while driving, it dips down to 20 Hg. Is this normal?

 

Yea if you are off the throttle it should be well into vaccum.

 

At idle it should be around -15in hg. If its closer to zero you have a boost leak most likely.

 

Yea your fine. Do a boost test just to be sure(if you dont know how to PM me). Remember, when your cruisin and you let off, your engine is still spinning the rpm it was at, meaning the cylinders are still drawing in air rather quickly and with the throttle closed that pulls a stronger vaccuum in the manifold.