Originally Posted by Manny Laureano

I have a suspicion you've grown out of your mouthpiece, Jorge, and your lips are rebelling.

Assuming things are as you say and the embouchure is not corrupted by any imbalances, I think there may be a few potential issues:

1) the throat size may be too small and you're encountering resistance you wouldn't have noticed on the old embouchure

2) the mouthpiece may be too small and not accomodating your lips anymore because you have different needs

3) the rim may need to be changed to accomodate the new embouchure and give you a bit more wiggle room

4) it could also be abdominal tightness which is VERY common in these cases, as well. That causes resistance that manifests itself at the lips and creates strained sounds.

Why don't you go on a mouthpiece sampling safari and see if anything makes sense. If you feel the mouthpiece you presently play is right for you, I don't have an answer without hearing you play.

Good luck,

ML