Bigger Pic
Here you go, I put the bottom of the template lower on this truck than what it should due to your pickup appearing to have a lift kit making it taller. By placing the template lower and making it bigger it compensates for this.
Notice you are shooting for a 10 or 11 inch "Lift Gate" above your bed. This makes for a 8° "slope" over all, with a 12° slope at the top of the tailgate/back of cap.
This will yield your best result.