Are you sure step-up applies? Was the person already acting as trustee for their trust (the trust already was the partner)? What type of trust is it? Revenue Ruling 2023-2 makes clear that there's no step-up in basis for assets in an irrevocable grantor trust. Or, did it pass through a revocable trust from the estate?

I think the default treatment is that the trust's INTEREST in the Partnership gets the step up, not anything withing the Partnership.

But there is an election (§754?) that can change that.

Are you making the election?  What exactly are you trying to calculate?

With that being said, I'm pretty clueless about Partnerships, so maybe Susan or somebody else may be able to point you in a better direction.