It´s so early that we might don´t even get Navajo, Navajo migrate from Canada to Southern USA/Northern Mexico in 1400 A.D., The introduction of the llama and Alpaca in the 700. A.D., the Butterflies are enormous, maybe we don´t see the Mayan collapse, as the llamas could give more food sources and the animals do really well in arid and drought stricken areas Thus a more powerful expansion of the Mayan culture to the north. It could happen that the introduction od the llama in the mesoamerica will mean a stop to the Human sacrifice as the Llama could become the favored sacrificial animal, as is a more scarce resource
It was that recent? But the area the Navajo immigrated to and their neighbours is good country for some alt-sheep raising (like llamas provide). It's definitely good the American Indians can get a domesticate other than dogs.
Alpaca are great too, since they basically are like sheep. I have relatives who own a property in rural New England which is down the road from an alpaca farm, so based on the climate there (get out by October), alpaca can thrive in a lot climates. This is definitely great for ethnic groups in the north of the US, where farming is minimal and they need to hunt and gather for additional nutrients. The alpaca (and presumably breeds of llama) can give milk and meat in those periods, plus extra pelts.
The potato is great, obviously, but IIRC indigenous farmers in the US South planted sweet potato, a great crop for the region, but still weren't able to keep a solid civilisation like the Late Mississippians (which collapsed regardless), which seems odd, since sweet potato was historically a very common staple crop in later years which many older Southerners to this day dislike since they consider it a poverty food. So new crops alone don't necessarily bring strength to a particular group.