It's not so much the speed, but the rpm that I got the problem and that's normally at about 3000-3500 rpm. I got a sudden drop and power like it just cuts itself off and then the rpm drops and it kicks by on. It seems like you may have a similar problem. Initially when I had the problem there were not CFL also, but after a few weeks of driving it, then it came on. I had two problems, the Mass Air Sensor and the Cam position sensor. Both of which I've changed out. If you elect to do that make sure you get OEM.
Unfortunately, both of these OEM products are freaking expensive!!! But it got my car running in the end and right now it runs like it brand new! So I guess it's worth it.
Have you looked at the fuel filter and the fuel pump yet? The fuel filter is cheap, so if you havn't done so, replace it. The pump on the other hand is a bit more, so you may want to narrow down the problem before going that route.
Good luck! And keep us posted on your results!!!