This appears to be a series of short stories, collected into one book as A Different Flesh, by Harry Turtledove.
Wikipedia describes the plot as:
The stories give a brief glimpse in this altered American history ranging from 1610 to 1988. The Western Hemisphere is inhabited by Homo erectus rather than Homo sapiens, as well as megafauna long extinct in the known world. Consequently, the colonization of the New World by Europe has been a far more difficult process. As time goes by, various characters debate the nature of the "sims" (as erectus is known) and their role in human history.
One story, "Though the Heavens Fall" matches the slavery story you describe (although, the outcome does not seem so good for the sims):
1804: A house-slave named Jeremiah goes on trial for running away, and his attorney presents the argument that, with the existence of sims, there is no need for human beings to enslave other human beings. They are successful, and the court's decision leads to the emancipation of all human slaves. There are echoes of the historical Dred Scott Decision.
The last story, "Freedom", is desribed as follows:
A group of sim's rights activists, including a great-great-granddaughter of Henry Quick, protesting experimentation on sims "rescue" Matt, a sim infected with HIV, from a medical lab but fail to take enough HIV inhibitor, which is medicine that suppresses the effects of HIV and AIDS. Eventually, this forces the activists to return Matt to the researchers."
It obviously involves AIDS as you describe.
Also, generally speaking, if a story is even a mildly famous alternate history story, Harry Turtledove is the author to look at and rule out first. :)