I practice daily, at least 30min depending on the time I have (I'm still a student). Not sure if I practice "sub optimally", I do slurs through my confortable range, I play scales, some arban, some studies etc. I guess I should try to do some warm-ups before I go to the lesson and/or flap my lips on the way to there . The teacher litterally said I have to warm up less. She also mentioned that sometimes you just need to be able to play when you don't have the time or place on a gig. But this is a bad argument IMHO... &Thanks for all the comments, I think I'll have to find the problem myself, lots of possibilities. I'll also talk albout this with an other teacher/professional jazz trumpeter.