Partial Cracking After Switching Horns

[tptLad]

Don't know if this is the right place for this type of post, so please redirect me if needed.

I just recently switched back from the horn my band director checked out to me for marching season to the other horn that I have had for the last 3 years. However, I'm having a hard time making the switch back and keep having constant issues slotting 4th and 5th partial, specifically f and f# top of the staff. Is there anything I can do about this, or it something that will just take time to adjust back to? My mouthpiece is the same, so that probably isn't causing the issue?
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"Life is a lot like jazz… it's better when you improvise." - George Gershwin