TromboneChat

As mentioned notes on positions 5-7 don't sound as resonent and clear as notes in the upper positions. I also find slotting issues in those positions. Could this be my fault or bad gear?

You may be shortchanging the positions just because your arm doesn't stretch that far. How are the corresponding F-attachment notes compare to 6 and 7 (C and B natural)?

The more I play out there the better they get. They will always have a slight timbre change, but then every note has one. (The other notes are just the ones we listen to all the time.) Try doing your workouts in every position. Fit glisses into your exercises so you can get from 1st to 6th and back on every partial. On slotting, the partials feel "closer" together so it can feel confusing to hit the right pitch when the same pitches also occur closer in. But doing flexies in 5 and 6 or a regular basis and fairly soon the confusion should sort out.

They take a lot of practice. However, a leaky slide will nullify all of that quickly. My first Edwards dual bore was so leaky that it had no 7th position.

Something I see a lot, because I recognize it, is this:

If your slide arm is pulling your horn to the right in outer positions, but your low range needs to be to your left, you could be moving your embouchure to where that range just simply doesn't work and will never sound good.

This is the sort of stuff I diagnose and fix in Skype lessons. You might figure it out on your own but most people don't.