Rear End Instability?

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Originally Posted by thstone

Shifting in a corner at 115mph will definitely upset the balance. Get your shifting done before the corner.

Bingo!
thstone has been getting some good training. When you are going 115 even in a gentle curve the tires are pretty heavily loaded. It's a physics thing. Lifting the the throttle and shifting mid corner is a good way to experience the thrill of going backwards out in the weeds at 115. If this does not make any sense to you, a spring DE or performance driving school might be a really good idea.