Looks like a heat-treating problem, maybe? Welcome to the world of racing and the world of after-market parts. Try not to be too pissed about it, it sort of comes with the territory. Upset and disappointed, sure. But not mad. I'm glad it didn't happen at half-track and spin you into the guardrail. Give the supplier a call, I would bet they will replace them for you and will want to do some research on their machine shop. Way to go for enjoying your car fully, not many guys do. Get it fixed and go snap a driveshaft! Don't know if you had any wheel hop, but feel for it and stop the spin/burnout if the wheels start to hop-that's a drivetrain killing situation.