Preheat the oven to 400 degrees F. Combine the peaches, brown sugar, ketchup, vinegar, soy sauce, garlic and ginger in a food processor or blender.
Pat the pork dry with paper towels and sprinkle liberally with salt and pepper. Reserve half (about 2 cups) of the peach BBQ sauce and set aside. Transfer the pork, fat-side up, to a rack over a heavy-bottomed roasting pan and brush the rest of the sauce all over the pork. Add the stock to the bottom of the roasting pan.
Roast the pork until a meat thermometer inserted into the thickest part reads 140 degrees F, about 1 hour.
For the smashed potatoes:
Meanwhile, place the potatoes in large pot and cover with salted cold water. The potatoes will soak up that salt like pasta and it will make a big difference in flavor. Cover and bring to a boil and cook until fork-tender, 20 to 30 minutes. Drain the potatoes, and return them to the same pot, allowing them to dry. Heat the half-and-half and butter in a small saucepot over low heat. Add the mixture to the potatoes along with the cream cheese and sprinkle with salt and pepper. Smash the potatoes with a potato masher and set aside, keeping warm until ready to serve.
For serving the pork:
Transfer the pork to a baking sheet to rest for 10 minutes, and then thinly slice half of the loin. Store and reserve the other half for leftovers.
Remove the rack from the roasting pan and place on the stove over medium-high heat. Whisk in the reserved BBQ sauce and scrape the bottom of the pan to incorporate the browned sauce. Cook until slightly reduced and thickened, about 10 minutes.
Serve the sliced pork with the reduced peach BBQ sauce and the smashed potatoes.