CaliPer. A precision measuring tool, although you don't need one that's all that precise. Ask at your local car parts store, or maybe a hardware store.

The thing is, if you have worn cam lobes, they're worn all the time and you wouldn't suddenly get good revving just after adjusting the valves -- I think that's a coincidence. It would also not drift between higher or lower rpm at steady throttle. A vacuum leak would do that at idle, but typically not at speed. So my thought is that you either have some restriction in the fuel pressure causing a lean mixture in sustained running, or very erratic ignition timing, or something like that.