Carnegie-Mellon, by any chance?
Regardless, when I had my audition there, I had to do some excerpts. I played the "Brisk Young Sailor" and "Lord Melbourne" movements of Lincolnshire Posy, "Bydlo" from Pictures at an Exhibition, and the "Cool" portion of Symphonic Dances From West Side Story.
Some good choices are Holst 2nd suite (like Dave mentioned), something from The Planets (Mars and/or Jupiter), any of the standard marches (Sousa and Karl King), or really anything out of Dave and Brian Bowman's excerpt book.
University of Miami - BM Euphonium Performance '21
Indiana University - MM Bass Trombone and Euphonium Performance '24
Besson Prestige 2052S
Courtois 551BHRA
Conn 88HCLSGX
Various Greg Black mouthpieces