Preheat oven to 350 degrees
Spray the loaf pans with cooking spray; cut a piece of parchment paper to fit the bottom of the loaf pan and place in the bottom, and spray again with cooking spray; this helps with removing the bread when it is done baking
Melt the butter and allow it time to cool to room temp; slightly warm is ok
Melt the chocolate and allow it time to cool so that it is only slightly warm
In a large bowl, whisk together the flour, both sugars, pumpkin pie spice, baking powder, baking soda, and salt
In another bowl, whisk together the eggs, sour cream, pumpkin, and vanilla
Stir the wet ingredients into the dry ingredients until combined
Divide the batter in half into separate bowls
Add the melted chocolate and sifted cocoa powder into one of the batters and whisk together until combined
Add the two batters into the two loaf pans alternating scoops between pumpkin and chocolate
Use a table knife to swirl through the batter
Make the streusel by mixing together the flour, two sugars, cinnamon, and salt into a bowl; drizzle in the melted/cooled butter; mix with a fork until the butter is combined, but do not overmix! You want to have big and small pieces
Top each loaf evenly with the streusel
Bake for 50-60 minutes, or until the center is set and an inserted toothpick comes out clean
Allow cake to cool for about 30 minutes before removing from the pan