I had a very similar problem with my mare. She's also all go go go go and usually goes with her head up in the air, very fast and very tense so we've been working on relaxing and going long and low to get her to just relax and realize that life isn’t so scary.
I also used to do a similar thing to you but I found that I just spent too much time in my mare's face and it just ended up with her getting more and more tense. So, we started over again. I'm not sure if this is technically the "right way" but it works with my mare.
Basically, I took away the rein aids completely. Kept contact with my mare's mouth and then, once she started to speed up, I would circle her and slow my posting, using my seat to slow her down, then the moment she slowed down and relaxed and dropped her head, I gave with my contact and brought her down to a walk - rewarding her by stopping 'the work'. The important thing is to keep doing it, keep asking with the seat and circling, making the circling smaller if needs be, until she responds. I initially made the mistake of thinking that if I brought her down to a walk, let her walk a little and then ask for the trot again, she would have ‘relaxed’ but I found out it wasn’t the case and I realized that I was ‘rewarding’ her for her fast trot. Once I started keeping her trotting until she slowed down and relaxed and only then allowing her to walk, we’ve come a long way.
Its taken me a while but we've gradually been able to build it up. From just asking her to relax to slow down, I began asking her for three or so strides in a nice long, relaxed frame before allowing her to walk, then for a whole circle. And it’s made a world of a difference. Now if she speeds up, I give the seat aids, and she almost always immediately slows down and goes into her nice relaxed frame.
As I mentioned earlier, not sure if this is the ‘correct way’ but I tried everything else (including making my mare trot and trot and trot until she was tired and slowed down but it never seemed to get across to her that a slow trot was what I wanted from the beginning so I abandoned that approach). But be warned, my method does take some time to be effective but my mare was getting the idea after a week or two.
Hope it helped!