The NH Historical Society has published a special issue on slaves in New Hampshire.

See:
Historical New Hampshire (Vol. 61, no. 1) Spring 2007
Dishman, Robert B. " 'Natives of Africa, now forcibly detained': the slave petitioners of Revolutionary Portsmouth." pp. 6-27

Dixon, David T. "Freedom earned, equality denied: evolving race relations in Exeter and vicinity, 1776-1876." pp. 28-47

Clark, Lynn and Rebecca Courser. "Rural free Black settlements in Post-Revolutionary New Hampshire: a study of five towns." pp. 48-67.