"The distribution my client, and other beneficieries, received was sales proceeds"

Then it's not Worthless; it's Closed. It's not Beneficiaries; they were the Partners. It's time to wrap it up, accordingly, for basis and gain. Or, one part went through the trust to multiple beneficiaries? It seems you have a number of data streams, because "The asset was placed into the Trust" would be the partnership interest? "My client inherited it upon death" seems like something that did not go through the trust, but what is the "it" here? The partnership interest went into the Trust, which had one or more beneficiaries? "the funds were distributed to my client per the will" seems like something did not go through the trust. In other words, anything per the will that bypassed the trust has different treatment.

"The gas wells were fully depreciated and the sale resulted in ordinary income reported on the K-1"

Exactly. That means nothing here applies to the trust or your client. This is Partnership activity.

"to the Trust and subsequently to my client" as the trust beneficiary.

"Since the asset that was sold did not receive a step-up in basis,"

But it wouldn't, anyway, since it was inside of the partnership. It seems your Client has not inherited any asset to have step up; the trust replaced the deceased as the partner. The interest in the partnership is what was inherited, or placed in the trust (I'm a bit confused here, sorry).

So far, anyway, that's what I am following.