I don't know much about these transmissions, at what point does the torque converter lock up in our 05+ auto trans cars?

I have a new torque converter (PI 3000 stall), and when under normal light throttle driving, the last two shifts (3-4, and 4-5) feel a little different than the first two shifts (1-2 and 2-3). Those last 2 shifts also bring the RPMs down probably 500RPM less than the first two shifts do, when under very light throttle.

The best way I can describe it, is that it feels like the transmission is physically locked to the motor output for the last 2 shifts. The last 2 shifts are alot more jerky feeling than the first two shifts. Is this when the converter locks up? I was under the impression that the lockup happened after the car was already into it's final gear, and didn't even ever happen durring a gear shift. After I'm in the final gear, I don't ever feel or hear any other changes in the rpm, just a steady climb.

I'm having a hard time trying to describe it, has anyone else noticed this? Does anyone even remotely know what I'm trying to describe? I haven't really ever rode in or driven any other 05+ mustangs, is this normal? I noticed it with the stock converter as well, just not as predominantly.

It doesn't feel like a higher shift pressure, but just to make sure I'm going to raise the shift pressure on the 1-2 and 2-3 shifts all the way and see if they feel more like the current 3-4 and 4-5 shifts. Right now it looks like they are all set to 0.