I powershifted my 88GT for a couple years with no related problems. It had 130k when I sold it.
I powershifted my 87GT for over a year before the tranny went out (I was actually being really nice to it at the time), in an unrelated deal. Both were totally stock driveline setups. (Clutch, quad, tranny, shifter)
Powershifting wears the syncros in the tranny. It doesn't hurt the gears, and as long as your clutch is adjusted properly, you shouldn't have any problems occationally powershifting.
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