Why are you shifting it is my first question..?

Let it shift for you. Once you have it in first, just get on it and hang on! The trans will shift when it needs to.

I experienced this at the track as well...and it was caused by wheel spin. If I spun the tires the car would jump into 2nd gear REALLY quick and I wouldn't even notice because the tires were spinning, I'd hit it to shift and I'd be in 3rd.

SQ