Re: C2, D2 key issues
I'm sorry, people use C2 in different ways. Do you mean the note on the second line above the staff?
If so, does the note an octave lower also have a fuzzy problem?
What do you mean, the octave mechanism bounces up?
If the key height is too low, that would change the intonation as well, and raising the key could make the note go sharp.
Some horns are just stuffy in some ranges, and little can be done.
Try different mouthpiece and reed combinations also. That may help.