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... I seem to remember that after the founders death, the church became trinitarian.

Yes, one portion did:

That group was led by Joseph Tkach.

He enlisted CRI to try to get their orthodoxy re-focused.

The rest fractured into 300+ groups (as this thread article mentions) in less than a decade. Most of the fracture was over "governance" issues; some of it was still highly doctrinal.

Here is the transformation of the portion of Armstrong's church that went Christian:
A Short History of Grace Communion International

They say:

Transformed by Christ

A Brief History of Grace Communion International In the early 1930s, Herbert Armstrong began a ministry that eventually became our denomination. He had many unusual doctrines. These he taught so enthusiastically that eventually more than 100,000 people attended weekly services. After he died in 1986, church leaders began to realize that many of his doctrines were not biblical. These doctrines were rejected, and the church is now in full agreement with the statement of faith of the National Association of Evangelicals. To reflect these doctrinal changes, in April 2009, the denomination changed its name to Grace Communion International. This name better reflects who we are and what we teach. For a press release, click here. For a letter of further explanation, click here.

Here is the story of how the church developed and how it changed. Transformation of a denomination

Jesus Christ changes lives. He can change an organization, too. This is the story of how the Lord changed our denomination from an unorthodox church on the fringes of Christianity, into an evangelical group that believes and teaches orthodox doctrines. The story involves both pain and joy. Thousands of members left the church. Income is less than one fourth of what it once was. But thousands of members are rejoicing with renewed zeal for their Lord and Savior Jesus Christ.

(You can go to above link to read a LOT more)