MAX has a good trouble shooting suggestion and it would be exactly what I would do... Remove the SB and see if the problem repeats itself... The SB should have no direct effect on your transmission shift points, nor should it cause disengagment at high RPM's because it only alters the throttle response curve. You might just have a "disassociated cause & effect" situation... Meaning that you have some underlying trans problem that is being exacerbated by you being more aggressive on the throttle since you installed the SB.

I'm not a tranny expert, but most often an auto trans will slip because of fluid flow issues (lack of, dirty, clogged filter, etc) or with the Crossfire, it can possibly be caused by a faulty transmission control module or transmission sensor... Those issues would be represented by DTC's in your computer...

Good luck...