I would first check your secondaries to be sure they are operating properly. The vac tube or some of the connectors may have a leak/crack that causes your secondaries to remain open.
Second thing I would check - plugs & wires. When was the last time you had them changed & what brands did you install?
Finally, I recall some posts in which people spoke of some popping. Search for the word "pop" in the last 6 months & see what comes up. This will likely offer some valuable insight.
Have a safe Holiday weekend.
