(I don't know how much redpointing you've done, but I found I got the same anxiety in the past, but didn't last time I went redpointing).
Good luck in Tarn!
I had almost exactly this on a couple of different routes. What helped me was defining the rest as x seconds of rest and start counting and shaking appropriately. No looking ahead to the rest of the route. Just focus on breathing, shaking, and keeping my head focused on the resting, not on the anchors. Once my mind stayed in the "now" it was much easier to stay focused on the rest of the routes.
Remember that you're climbing a bit of rock, and if you onsight 9b, you've still only climbed a bit of rock.
On my two latest sport trips i suffered some form of redpoint anxiety, and wonder if smeone else has the same or knows a strategy to work around it.