Elevation factors into manifold vacuum as well.
If compression test was done with engine at operating temp I'd next do a 'wet' compression test or a cylinder leakage test .
For those ‘bolters that don’t know what a wet compression test is, after your initial readings, inject about a teaspoon of oil into the cylinder the repeat the test. Don’t inject more that a teaspoon of you may get false results. If the compression comes up significantly (over 10%) it’s the rings. If no increase, it’s the valves.
