Bring 2 cups broth, reserved neck and giblets and trimmings to simmer in Dutch oven over high heat. Cook, adjusting heat to maintain a simmer, stirring occasionally until all liquid evaporates and trimmings begin to sizzle (about 20 minutes). Continue to cook for 3-4 minutes until dark fond forms on bottom of the pot.
Reduce heat to med-high. Add onion, carrot, celery, parsley, thyme, garlic pepper and salt. Cook until onion is translucent, 8-10 minutes.
Stir in wine and bring to simmer and scrape up fond. Add remaining 4 cups stock and bring to simmer over high heat. Reduce heat to med-low, cover and simmer for 1 hour. Strain through fine mesh strainer. Can be refrigerated at this point for up to 2 days.
Make roux and cook, stirring constantly over med-high until deep golden brown (5-8 minutes). Reduce heat to low and slowly whisk in strained stock. Increase heat to med-high and bring to simmer. Simmer until thickened (5 mins). Add drippings if using and thin with extra stock if required. S & P to taste. Can be refrigerated up to 3 days or frozen for up to 2 weeks.
Reheat, bring to simmer over med-low heat, stirring occasionally.