The GTs. They suck, no they really suck, no they really really suck.Were you running the PR4GT tires? Or just the PR4 spec on the K16GT.
I'm surprised that you hated them and they "stepped out" on you. I'm having very good performance from mine and I have pushed them pretty hard.
Almost high sided the bike twice. But the low siding was worse. I cant say enough bad things about the tires.