Every time I start making around 6k the car just stumbles like a **** and just doesnt have any power until it shifts. After the shift it is fine until it has to shift again. What oculd it be? I have pretty black plugs but this just started. It didnt do it 3 weeks ago when I took it to the track the first time.

 

Are you sure you're not bouncing off the revlimiter? A few other possibilities could be a slowly dying fuel pump, bad coil, or dirty fuel filter.... Good Luck