Put the grapes on a perforated grill sheet or in a grill basket and grill over high heat, tossing occasionally, until they just start to burst, about 6 minutes. Transfer to a plate to cool completely.
Meanwhile, grill the peach wedges over high heat, turning once, until lightly charred, about 6 minutes. Transfer to a plate to cool completely.
Combine the wine with the simple syrup, tequila and grilled fruit and stir well. Refrigerate until the sangria is chilled and the flavors are blended, at least 1 hour and up to 8 hours. Serve the sangria over ice.
You can also cool the grilled fruit, then freeze it to help keep your sangria extra cold.