How are slave narratives written before 1836 different from those written after 1836?

Slave narratives had existed in various forms for many years prior to the 1830s. Despite some inevitable differences between individual testimonies over time, it is possible to identify certain general themes and characteristics that distinguish them from those made and recorded after the Civil War.
In the 1830s, slave narratives tended to resemble classic statements of conversion; they were primarily accounts of spiritual testimony that meticulously detailed the systematic ravaging of the soul by slavery and all its horrors. Earlier examples include the preacher George White's A Brief Account of the Life, Experiences, Travels and Gospel Labors of George White, an African; Written by Himself and Revised by a Friend.
Spiritual autobiography was a highly popular literary genre at the time. In using a conventional Anglo-American literary genre to tell their stories, African Americans attempted to induce some degree of sympathy from their white readership, especially those in a position of power and responsibility.
As well as sympathy, slave narratives inevitably aroused hostility. Slave owners, Southern politicians, and their apologists in the press accused slaves and their white amanuenses of at best exaggerating, and at worst lying, about life under the "peculiar institution."
In response to this, writers of slave narratives started to pay more attention to matters of proof. The greater the veracity of such stories, the harder it would be for the defenders of slavery to undermine their credibility in the court of public opinion. This necessitated a radical change in the nature of slave narratives. Increasingly, they were now seen as documents of fact rather than expressions of personal experience.
In this significant shift we can see the extent to which slave narratives reflected changes in American politics and society. Though still outwardly a deeply religious country, the United States was also imbued with the scientific spirit of the mid-19th century. The scientific mindset dictated that facts were of overriding importance, not just in relation to the natural sciences, but also to historical scholarship.
With the end of the Civil War and the passing of the 13th Amendment, it was necessary for slave narratives to have a different focus. Slavery was to be seen not just as an embodiment of repression and degradation but as a trial. African Americans had emerged after years of hard, bitter struggle, fighting for their freedom on the battlefield and proving themselves in positions of political responsibility during Reconstruction.
The rapidity of industrial change after the war added a fresh impetus to this process. In an ever-changing economy requiring increasingly complex skills, it was essential to African Americans that they too were able to participate successfully in this new economic order. The cutthroat world of capitalist competition would provide a testing ground for African American workers, in which they too had the right to live and work as free men and women. The challenge here was not just to contradict the prevailing prejudice of white supremacy, but also to take on and disprove the racism dominant in various scientific fields. In a country in which social Darwinism was becoming increasingly influential, it was essential for African Americans to prove that they too could survive and prosper under new economic realities.
Postbellum slave narratives contributed enormously to helping African Americans find a place for themselves in the new America. The apogee of this struggle was reached in Booker T. Washington's classic Up From Slavery of 1901, a personal success story which extolled the virtues of economic and educational progress. As well as contributing to a more confident self-image among African Americans, slave narratives such as Washington's also forced white America to take claims of racial equality more seriously.