If you have bad attacks and feel tight when you play a big part of the solution probably lies at the place between the inhale and exhale. If this is not something you've concentrated on, you probably have a gap between your inhale and exhale which you would not have if you were breathing without the trumpet. In this gap, you are tightening your glottis (this is the thing that you can close in your throat), compressing your air behind your tongue, and probably squezing your lips together. To fix this you need to focus on not letting there be any space between your inhale and exhale. This will feel unsettling at first, but you just have to trust that it will work. When doing this think about not allowing any air compression to build up. Your tongue moves with the air like you are speaking. A lot of people have a tendency to pull the tongue back and then articulate. Avoid the pullback, and just articulate. This should be a continuous free flowing system in both directions.