The battle of Vicksburg and the Battle of Gettysburg were both turning points in that they showed, in very different ways, the ways in which the Confederate Army was vulnerable.
At Gettysburg, the Union Army defeated the Confederate Army in Union territory, showing that the Confederate Army was not successful outside their homeland.
Vicksburg showed that the Confederates could be catastrophically defeated in their heartland and that the Union Army could bring a major siege and make life difficult.