Afaik the FG utilises a different torque reduction strategy for upshifts. There are details on the PCMTec forum.
What is more likely happening in your case is is actually hitting the limiter, as well as displaying the shift characteristics. When you raise the power level, a usual side effect is the transmission isn't able to make the shift before hitting the limiter. You can tune the trans to tighten it right up and shift properly, while a better solution is to raise the rev limiter by 200rpm so it doesn't actually tag it.
Do not hit the limiter with stock oil pump gears, you're better off raising it high enough so you don't touch it.