Ok so I'm playing second trumpet for my school's adaptation of West Side Story! It's awesome, a lot of fun. However, a lot of parts say "D Trumpet". And I'm like "wtf this is a B flat" and my directer tells me to transpose is 3 steps up. Problem: I have to play like, F sharps. Um. I've been working on my range A LOT with my 3D and normal B flat trumpet... and it's getting better but not THAT much better.

So I just looked it up, and apparently a D trumpet is higher than a B flat trumpet. Much higher. So I'm thinking to myself "well my band director wants me to stay on this trumpet, which I do agree with no doubt, but I don't want to get there and have to play it an octave down". So what can I do? Should I maybe look into renting a D trumpet? Would that be even possible?

It just depends on how well you can transpose. If you can transpose very well, just keep doing that. If not, its your decision, but it seems like a lot of money to pay just to keep from transposing. It's up to you though.

It's not just the transposing, it's the range of these notes. I mean I'm not bad, but I can't really hit a high F# in song. I'm just saying if I should rent one for these parts (that say D trumpet anyway) to make it maybe easier to play them... this way I play them right instead of an octave down (still right but not the same effect).

even if you rent a d trumpet its not gonna make the high notes easier to play. I would suggest working on your high range on the Bb at the parts you cant get all the time. Write out the parts that you cant transpose in your head. If you did get a D trumpet you would have a really hard time with note placement because the notes arent where you expect them to be. No one just switches. If you do switch i would highly suggest listening to the pieces as much as possible to hear where the notes are and practice the Clark studies switching from Bb to C so you get the idea of how much each note changes.
Good luck

Oh alright, so it's like that. Yeah I don't really know these things, hence I come here.

But eh, if it's going to like take a while to learn how to play it since it's different like that, renting a D trumpet wouldn't even be the smart thing to do... Damn... Oh well I'll get it.

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EDIT: When I say I'll get it, I mean the music, not the trumpet lol

I'm surprised you're getting parts in D within your highschool. You probably have a pretty decent music program I'm guessing?
Practice your range, playing on the instrument whereas you won't have to transpose won't make it easier to player higher. It'll be easier to hit the note (meaning you won't accidently hit another note in the register) but it won't be any easier to be able to play in that upper register. An easier way to transpose with a Bb trumpet to D is to play the major 3rd. The second note within an arpeggio. i hope i did some helping. keep practicing!