How do I lock a 4l60E in 3rd on the dyno?

This is my second auto that I have tried to tune on the dyno to no avail. I can't get these things to stop down shifting to second. I tried leaning into it. I tried high rpms. Nothing works. The first car I did was a Corvette and now a TA. What is the deal? I manipulated every trans table I could find but that thing just keeps down shifting when you mat it.

Using the Scan tool's Bidirectional/DVT tools, you can force it to hold 3rd gear without having to adjust the tune.

Thanks. I will look into that.