Place ham in a slow cooker. Set aside.
In a medium saucepan, combine cola, brown sugar, mustard, cinnamon, cloves and garlic. Bring to a boil over medium-high heat, stirring often. Reduce heat to medium-low, and simmer uncovered for 20 minutes (to allow glaze to reduce), whisking frequently. Remove garlic cloves.
Pour glaze over the ham. Cover and cook on LOW for 3-4 hours, or until a thermometer registers 140 degrees F when inserted into the thickest part of the ham. Transfer ham to serving platter.
Pour liquid from the slow cooker into a medium saucepan. In a small bowl, whisk together cornstarch with 4 teaspoons of cold water. Add the cornstarch slurry to the saucepan. Bring to a simmer over medium-high heat, and cook (stirring regularly) for 6-8 minutes (or until thickened). Pour glaze over ham and serve!