I think there is some confusion, because if you read Andy's original post, the graphs are from two different cars.

He's asking why the launch on the top graph as it transitions from 2 step to stall speed is so rounded off and slow to get there.

The second graph from a different car is just an example of what he thought it would normally look like with a small "spike" after the two step comes off and then it settles in. (which as noted, in this case the driveshaft speed is showing a spike indicating spin also, but that's aside from the question).

As mentioned getting the two step up close to the stall speed will do this. Also if it's in this high 2 step leave, and it dead hooks... it can also cause really really high load on the motor so it won't transition clean off the two step.

I'd try lowering the two step first, but you might need to play with the suspension a little to help it spin. Depending on what it's doing it might like less air in the tire to let it get some wheel speed, or maybe even tighten up the rebound on the shock so it doesn't hit the tire so hard.

Andy you are right it could probably benefit from a slightly looser converter, and slightly more RPM on the shift too, but I don't think that's causing the issue you're pointing out.