Hey there @buekmann, Lips slurs are the trickiest thing to do, especially when you are starting out.
You must be really patient and spend most time making the best sound you can. Develop the slurs slowly each day without forcing. I don’t mind you looking ahead to more advanced material to try out but at this stage spend most of your time reinforcing the basics.
Are you humming a lot? Are you doing the BCH breath with your eyes closed. You must do this several times every day. Are you sure you are doing the PASSIVE balloon exhalation rather than forcing?
The throat will tighten when you either force the air or clamp the lips or worst still, BOTH. Really have that magnifying glass out and notice when things become difficult; at what pitch and at what speed do you lose the purity in sound.
The 3 main points of the aaaahooooh exercise are to 1. eliminate pinching the lips by 2. recognising the Aperture Corners and 3. experiencing the sensation of playing freely – like singing.
It takes months, not weeks to develop on the trumpet, especially with pure PROCESS but taking your time now will offer huge benefits in the long run.
I can’t really comment on your gear but I suggest that is unlikely to be the problem however better instruments are slightly easier to play of course, but you need to know what you are doing to notice the difference.
Take your time and enjoy making a beautiful sound then slowly build it up.
Best Wishes and thanks for using WindWorks.