Make the pickled peaches: Place peaches and onions into a large bowl. Combine the vinegar, nectar, brown sugar, crushed red pepper and salt into a medium saucepan and bring to a boil. Pour over the peaches and onions and toss gently to combine. Cover and allow to sit for at least 2 hours, preferably overnight.
Make the chipotle BBQ sauce: Place all ingredients in a small saucepan and bring to a boil. Reduce the heat to maintain a simmer and cook for 5 minutes. Transfer to a blender and purée until smooth.
Make the rib rub: Mix all ingredients in a medium bowl and set aside.
Make the ribs: Heat oven to 350°F. Remove ribs from the refrigerator and allow to get to room temperature for at least 1 hour. This will allow for a better sear while baking and the spices will penetrate meat better as well.
Season ribs all over with the rub and place on a foil-lined baking sheet, bone-side down. Cook the ribs until they reach an internal temperature of 165°F, about 1 ½ hours.
Remove the ribs and wrap in foil. Continue baking until they reach an internal temperature of 195°F, about 25 minutes more. For more tender ribs, cook to an internal temperature of 203°F, about 30 minutes. Rest for 20 minutes, then remove from the foil and transfer to a cutting board. Cut into individual bones and place back on top of the foil lined baking sheet.
Turn the oven to broil and brush with a thin layer of bbq sauce. Broil until the sauce cooks into the meat, about 1 to 2 minutes. Remove from the broiler and finish with a little more rub. Serve with the pickled peaches.