350 timing problems

[C101971]

Now I know this is a commonly asked question and I had an answer but now I can't find the thread. Anyhow, I've timed my truck, a 71 c15 4 speed stick, however, it idols great and all is well till about 4 grand on the tac then she seems to redline. A month ago she would blow past 4 grand. I noticed the sticker in the bay says 4° for manual trans at 550 RPM, but everyone is telling me to do it at 8°. Kind confused here if someone could clear the air