Mix the preserves, balsamic vinegar, and allspice in a small bowl. Reserve half of the mixture.
Brush 1/2 of the mixture on the pork tenderloin, covering the entire tenderloin.
Cover and cook the tenderloin for 45-50 minutes, or until a food thermometer reaches 145 degrees F.
While the tenderloin is cooking, heat the olive oil in a skillet over medium-high heat. Add the shallots and saute for 1-2 minutes or until tender. Add the cherries, cayenne, and the reserved preserve mixture. Let simmer for 8-10 minutes or until sauce has thickened.
Using an immersion blender, food processor, or regular blender blend the dark cherry sauce until it is smooth. Be careful with the hot liquid.
Slice the tenderloin and spoon the dark cherry sauce over top. Enjoy!