[oleyellar]

What you are experiencing is the first critical harmonic frequency of the valve train, or what we always called valve spring float. I went through the same issues, mine quit a 5200 RPM. It felt just like the MSD rev limiter chip.
Here is a part of a technical paper I found from Crane cams.

I found this in Crane Cams info.
"A more important fact about spring rates, however, is the fact that the spring rate is related to the harmonic characteristics of the spring. As a general rule, the stiffer the spring (the higher the spring rate), the higher in the RPM range that the first critical spring harmonics occur! What this means is that a low rate spring (300-330 lbs./in.) will probably encounter a critical harmonic relatively low in the RPM range (4800-5600 RPM depending upon valve train component weight and lobe profile). If a critical harmonic occurs with your valve springs, the valve motions will momentarily be out of control. This critical harmonic will often be misdiagnosed as an ignition problem or fuel problem.."

I had tried everything that has been suggested in the previous posts and nothing helped. I changed valve springs, increased seat pressure slightly and added about 25Lbs additional pressure at full lift and the problem went away.

Google search for valve spring critical harmonic reasonance frequencies and you will get some interesting information. Check out the U tube videos of the " Spin Tron" valve spring tester and you will see what is causing your problem.
Good luck.