Don't you have to change your speedo gear with a new ring and pinion? What are your facory gauges reading when your car falls on it's face? Is it cutting out, like it's missing, when it reaches the 4k? If it's cutting out, or missing, that's what the rev limiter sounds like in my car, but I have an MSD with the rev limiter set at 6K so it might sound differen't then when I had the factory setup.
