Guys, this isn't a shift light that tells you to shift as you reach redline; it's meant for fuel economy. If you're driving around normally (not with the pedal on the floor) it will tell you when to shift to maximize gas mileage. That's why it only works with the throttle setting in normal on the M3. If the car is accelerating, it's not going to tell you to shift. But as your rate of acceleration for a given throttle position begins to taper off, it tells you to shift.
I coded this on my car and only kept it for a day. It's next to worthless on the M3; that car isn't meant to cruise around at 1,500 rpm in 4th gear. I found real-time mpg (DIGITAL_KVA) to be a much better solution.