That's an odd one. A shift kit should "speed up" the shift. But then, the new higher stall converter will likely "slow down" the shift. I use quotes because I'm referring to commanded vs actual shift rpm. At any rate, you probably do have to adjust the PCM since you did change the combination you're running and that causes it to both drive differently and react to shift commands differently.
Have you tried dropping the shift rpm and mph a bunch to see when it does shift or if it will shift? Test something like 4000 rpm and 0 mph. The mph could be biting you now because the new converter might be causing a lower mph at your shift rpm. First thing you've got to do is ensure you can control the shift points. The builder screwed something up that he needs to fix if you can't.
You shouldn't be hitting the stall wall - basically at launch you get a code and then it hits rev limiter and shifts 1-3. That should only happen on a 3000+ rpm stall. No codes, right?
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