Let the ham stand at room temperature for 90 minutes.
Preheat oven to 275 degrees F. Set the rack at the lowest position. Rinse and pat dry the ham. Using a sharp knife, score the skin of the ham in a criss-cross pattern. Place ham in a roasting pan. Pour just 1 1/2 cups of the cola and 1 1/2 cups of grape juice into the pan and add additional water if necessary to bring the liquid level to 1/2 inch. Cover the pan tightly with tin foil.
Roast in oven for 2 3/4 to 3 hours (about 15 minutes per pound) or until the internal temperature of the ham reaches 100 degrees F.
While the ham is cooking, prepare the glaze. Combine the remaining 1 cup grape juice, 1 cup cola, the juice from the pineapple (reserve the pineapple slices for later) and the brown sugar in a small sauce pot and simmer on low for 20 minutes, until it becomes thick and glossy.
Let stand at room temperature until ready to use (as the glaze cools, it will thicken up, making it easier to brush on the ham).
Take the ham out of the oven when it reaches the first internal temperature of 100 degrees F. Turn the oven to 425
degrees F. Brush the ham with about 1/4 of the glaze all over. Use toothpicks to stud the ham with the sliced pineapple, if desired. Once the oven comes to temperature, return the ham, uncovered to oven.
Bake for 15 minutes until the liquid is bubbly and the ham has turned to a nice, deep golden brown. The internal temperature of the ham should be 140 degrees F.
Remove ham to a cutting board and let rest for 15 minutes.
Return the remaining glaze to the stove on medium-low heat to warm the glaze up for serving. Carve and slice the ham, drizzle a bit of the cola glaze on each plate.