You need some local help. If your playing is so twisted that the tuning slide needs to be pulled out way more than normal, somebody needs to look at your face and breathing in a serious way. It is interesting to know to play relaxed and stuff about how this all works, but if you got into this mess, you need the way out and that means a teacher. I too think that this has to do with the braces. To prevent pain, you have most likely learned a less productive way to play trumpet. That leads to problems in tone production and tuning. It is possible to play well with braces.