RoccoNut16v

First of all, I've been playing on a Bach 7C until just this month, when I switched to a 3C. I switched by accident really! Marching practice, I was running late, and reached for the wrong mouthpiece (it came with the horn for free). I noticed it seemed to give me a better sound, so I'm sticking with it for now. My range seems to have dropped off a note or two, and my endurance has taken a slight hit, so that begs a question.

How big of a role is mouthpiece selection in endurance, range, tone, ect? I'm a 1st part player, and tend to take things up an octave regularly, (middle C is typically at the lower end of my part, though all players should know that). Should I even allow myself to consider a different piece to increase my range specifically? I feel guilty looking to switching mouthpieces to ease (NOT FIX) some of my, for lack of a better word, weaknesses (range specifically).

So what I'm asking is, can I increase my range with a new mouthpiece? Should I do it? I'm willing to sacrifice a bit of my lower range for upper, again because thats where I spend my time. What else will I lose if I switch for range? Will my tone/intonation suffer?

BTW, I'm quite naive in this subject, specifically because I refused to let myself explore mouthpieces until now. I noticed a lot of my peers getting caught up in selecting horns and mouthpieces, instead of attacking the problems themselves, which completely scared me away from changing anything, resulting in my relying completely on practice and development. I feel safe enough to explore a bit now though, and frankly curiousity is getting the best of me!

Thanks a ton, hope I'm not being too ambiguous in my questions.