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.
Something to Try
I am constantly experimenting with my students to find the best ways to teach them. I have been trying something new for the past few weeks that has led to immediate improvement for many of my students, including some huge range jumps and great improvement in accuracy and attacks. All you do is try to keep the tip of your tongue against the bottom of the bottom teeth at all times. Articulations are done on the bottom of the top teeth with the part of the tongue just behind the tip. As you ascend, push your tongue harder against your bottom teeth. Just mess around with it for a few minutes and see what happens.
How a Trumpet Should Sound
It is tempting to try to describe it and analyze it, but for your own good I will refrain for the most part. I just want to point out two things. First, it is never forced. It is always a piano singing sound (that doesn't mean that it is always piano, just that it keeps that relaxed, resonant quality). Second, hear the clarity of the articulations. Enough of my rambling. Just listen to what a trumpet should sound like.