I'd be suspicious of a vacuum leak too, replacing all the vacuum hoses is a real cheap place to start. A compression test is a good tool, but to really diagnose a sad engine you need to do a leak down test. Follow this link for instructions on how to build and use one. They are cheap to build, and considering the cost of the project well worth the time to make and will tell you for certain if you have ring or valve problems, and where.
Which is pretty cool for a tool that costs less than $30 to make.
Building and Using a Cylinder Leakdown Tester
Good luck, keep us posted!