My (jumper bred) mare is a rocket. Described by an Olympian as a Ferrari, she wants to do everything fast. She's sensitive, she's smart, and every round is a jump off to her! This does not translate well to eventing dressage, where I find the dressage judges give us very poor scores. And the harder I try, the worse it gets (surprise!)
She is on magnesium, no grain, and gets magnesium baths before dressage and after cross country. She gets ulcer meds before and during shows. On arrival at shows we lunge until her head starts to come down (10-15 mins) and do lots of handwalking. We have a brand new saddle, a very lightweight titanium snaffle that she appears to like (after trying many bits), and I don't believe she's in pain because my vet is very nitpicky.
I do lots of breathing exercises (me) and try to focus on a veeeerrry slow tempo, but in our current test we have lengthened trot, and lengthened canter, and that's SO EXCITING. I am happy to report the last judge said we were going too slow (!) ... but still with tension.
We went to a dressage show to try and perfect the warmup. Over two days we did 6 tests, lunged twice, and she was still a rocket in the canter! She's... fit...

At home, she can be pretty relaxed. In training, I always stop when things get too speedy and walk, or just stand, until she sighs. During lessons she spirals up, until I ask my trainer if I can stop and let the adrenaline out.
Any suggestions AT ALL?