For clarity: this is based on piaac test results. The literacy test results are sorted into 6 categories (1-5 and <1) for comparing the distribution internationally. 54% of Americans score less than 3, compared to top-scoring Japan and top-english-speaking Australia at approximately 35% and 45%. The task description for level 3:

Adults at Level 3 are able to construct meaning across larger chunks of text or perform multi-step operations in order to identify and formulate responses. They can identify, interpret or evaluate one or more pieces of information, often employing varying levels of inferencing. They can combine various processes (accessing, understanding and evaluating) if required by the task . Adults at this level can compare and evaluate multiple pieces of information from the text(s) based on their relevance or credibility. Texts at this level are often dense or lengthy, including continuous, noncontinuous, mixed. Information may be distributed across multiple pages, sometimes arising from multiple sources that provide discrepant information. Understanding rhetorical structures and text signals becomes more central to successfully completing tasks, especially when dealing with complex digital texts that require navigation. The texts may include specific, possibly unfamiliar vocabulary and argumentative structures. Competing information is often present and sometimes salient, though no more than the target information. Tasks require the respondent to identify, interpret, or evaluate one or more pieces of information, and often require varying levels of inferencing. Tasks at Level 3 also often demand that the respondent disregard irrelevant or inappropriate text content to answer accurately. The most complex tasks at this level include lengthy or complex questions requiring the identification of multiple criteria, without clear guidance regarding what has to be done

I could not find which source originally cited level 2 as "6th grade" equivalent, though the oecd recommends against drawing that parallel.