Manny Laureano

I'm going to venture you're mouthpiece is too small and you're not vibrating maximally in the lower register. That's the crux of all problems on trumpet, improper vibrations and the lack of balance to the airflow. That problem has MANY root causes and here it could simply be a rim/cup/lip relationship that is uncomfortable once you get to the lower register.

You shouldn't look much different playing a G above the staff as when you play a low G (that's a two octave distance).

I wish I could give a more comprehensive answer but i have to go to rehearsal right now. Think about what I wrote and let's continue the conversation.

ML