One thing that's so interesting about Gettysburg is how many Confederate generals fucked Lee over. He wasn't kidding when he said that losing Jackson was "losing [his] right arm."
General Ewell could have apparently just walked up to Cemetery Hill and taken it, virtually unopposed - indeed Lee had seen the hill and ordered Ewell to take it "if practicable" but Ewell chose not to.
Then there was Stuart running around trying to get himself in the newspapers instead of scouting for Meade. Imagine if Lee had had Forest in charge of his cavalry instead!
I agree, I think it's better to view slavery as the overarching issue that exacerbated these other tensions. Without slavery they wouldn't have been anywhere near as serious as the South's differences on tariffs and the role of the federal government in the states were driven by the economics of the slave system.
There was also a different view of the relationship between states and the Union compared to after the war that placed loyalty to one's state above loyalty to the United States as a whole. Lee and many other Confederates acted on this loyalty way more than any support for slavery even if they still condoned the institution itself.
People often forget slavery was still legal in the border states and slave territories that remained part of the Union until the passage of the 13th Amendment after the end of the war, the Emancipation Proclamation only applied to occupied Confederate territory. Many slaves in these areas had been freed or emancipated prior to this due to the effects of the war but there were still some who remained enslaved until then.
