Ok, let me get this straight. You are going to discount the opinion of your teacher who actually gets to see and hear you play, and seek advice from those of us who will try to diagnose your problem without getting to hear or see you play? From the situation you describe, it sure sounds like your teacher is right on the money. Brass playing takes time. Embouchure strength will build over time, as will your efficiency. Bone playing is actually quite simple, and requires 3 basic things.
1. Buzz the right pitch
2. Breathe properly
3. Have the slide in the right place.
I suspect your problem has more to do with 1 and 2.
Again, work with your teacher on this. Your problems aren't falling on deaf ears, I promise. I can sympathize, as trombone playing is a long journey, and road blocks can be very frustrating. Keep at it, and good luck.

Also, relax while playing. If you are pinching or pushing hard to get that note out it's going to sound like ass. Relax, and work your way up to it. It will come naturally and smoothly if you don't just go for it and work your way up there instead. Good luck, and don't let yourself get frustrated, you'll get there!

What is it with all the dirty languange in this thread? "God damn B flat?" "Sound like ass?" This is a trombone forum, not a porn site.

Don't get discouraged if you haven't been playing that long. Your embouchure might not have the strength yet to play in tune in the higher ranges. Just keep practicing every day and you will be fine. And listen to your teacher. He seems to know what he is talking about.

If you're still new to the thing just chill for a bit. Also realize that not all the notes in first play in true first. IF you play the 5 notes you listed in a true 1, the F will be sharp and the D in some cases may be a bit flat (I started playing some D's in 4 so I could mess with them more, then I just tuned my horn flat so I play first about a quarter inch out, flat first a bit beyond that and I can tune stuff). Depends on the player. Don't sweat that stuff at this point, we all have issues like that. Shoot for years I couldn't make the D above the staff come through to save my life, but now it comes through loud and clear. Listen to your teacher. My B flat in the staff is massively flat, I've been playing for 6 years. As soon as I made some physical changes some new problems crept in, thats just how it goes.