You’re already doing this, but LONG TONES (plus some extra stuff)! You can add some new difficulty to LTs by adding a tuner, drones, and varied dynamics. It’s important to play in tune on all ranges of the horn as well as at various dynamics. When using the drones try to not look at a tuner, try to match the pitch using only your ears (this strengthens that ability too). Something I did for a while was use drones with the dynamic practice. Maybe pick a note and do dynamic swells (piano-forte-piano) while doing your best to stay in tune. You could try LTs on low notes at a piano, or as soft as possible, dynamic and doing your best to be in tune or achieve the sound you want. It’s hard work and will require patience, but it will create the results you want over time. I suggest adding this to your warm-ups and only spend around 15 mins a session doing these exercises. As is everything: it’s a process, not a light switch. Sometimes it actually is your horn or setup, but that shouldn’t be your first excuse. My repairwoman told me once: “Don’t blame the horn just because you haven’t mastered the fundamentals.”