Preheat oven to 375°F Drain peach slices, reserving 1/2 cup syrup. Cut the peach slices crosswise into thirds; set aside. In a large saucepan, combine reserved syrup and cranberries. Bring to boiling; reduce heat to medium. Cook, uncovered, until the cranberry skins pop, stirring occasionally (about 2 minutes).
In a small bowl, stir together sugar and cornstarch. Add sugar mixture to the cranberry mixture. Cook and stir until thickened and bubbly. Remove from heat; stir in the peaches. Set aside and keep warm.
In a medium bowl, stir together flour and salt. Using a pastry blender, cut in shortening until pieces are pea-size. Sprinkle 1 tablespoon of the water over part of the mixture; gently toss with a fork. Push moistened dough to side of the bowl. Repeat moistening dough, using 1 tablespoon of the water at a time, until the dough is moistened. Divide in half. Form each half into a ball.
On a lightly floured surface, flatten one dough ball. Roll from center to edges into a 12-inch circle. To transfer pastry, wrap it around the rolling pin; unroll into a 9-inch pie plate. Ease pastry into pie plate, being careful not to stretch pastry. Trim bottom pastry to 1/2 inch beyond edge of pie plate.
Roll out remaining pastry to a 12-inch circle and cut into 1/2-inch-wide strips. Fill pastry-lined pie plate with cranberry mixture. Lay half of the pastry strips 1/2 inch apart on top of the filling. Arrange remaining strips 1/2 inch apart on top of the first strips in a diamond-shaped pattern. Trim ends of strips even with edge of bottom pastry. Press ends of strips into crust rim. Fold edge of bottom pastry over edge of strips; seal and crimp edge as desired.
Bake for 40 to 45 minutes or until filling is bubbly and pastry is golden brown. Cool on a wire rack at least 2 hours. Serve warm, or to store, cover and let stand at room temperature for up to 24 hours.