1. Heat grill to medium-hot. Place pork tenderloin, wine, garlic, 1/4 teaspoon each of the salt and pepper and the sage in a glass dish. Marinate, turning, at room temp for 10 to 15 minutes.
2. Bring sweet potatoes and ginger to boiling in a medium-size saucepan filled with lightly salted water. Cook 12 minutes, or until fork tender.
3. Meanwhile, transfer pork to grill, reserving marinade. Grill over medium-high heat for 12 to 15 minutes, turning twice, until thermometer registers 145 degrees F.
4. Pour reserved marinade into small saucepan. Whisk in 1/3 cup water, the flour, mustard and sugar and bring to a boil over medium-high heat, whisking occasionally. Once sauce boils, simmer 3 minutes; remove from heat.
5. Drain sweet potatoes and transfer to a small bowl. Add milk, butter, remaining 1/4 teaspoon each salt and pepper. Mash until fairly smooth.
6. Remove pork from grill; let rest 5 minutes before slicing on the diagonal in 1/2-inch-thick slices and serving with sweet potatoes and sauce.