Dry the venison shanks with paper towels and season them with salt and black pepper.
Heat a large skillet over medium heat and add the cooking oil. Once the oil is hot and lightly smoking, add the shanks. Sear until dark golden brown on all sides. Work in batches if needed to get a good sear.
Remove the shanks from the pan and place them in the slow cooker.
Turn the heat to the pan on low. Add the red wine to the pan. Scrape up the browned bits from the bottom with a sturdy spoon or spatula. Pour the wine over the shanks.
Add the remaining ingredients to the slow cooker. Cover and cook on low for 10 to 12 hours, or until the meat is fork-tender and pulls easily from the bone.
NOTES
Make sure the shanks fit: Check to see if the shanks will fit in your crockpot before starting.
Brown the shanks well for a better sauce: Pat the shanks dry, season them with salt and black pepper, and sear until dark golden on all sides. This will take your sauce to new levels.
Use bone-in shanks if possible: Boneless shank meat will work. But for the best flavor, use bone-in. If you're using boneless, I would start with around 1 to 1.5 pounds of meat.
Cooking times may vary: Most shanks take 10 to 12 hours on low, but older deer, larger shanks, and whole shanks can take longer. The meat is ready when it pulls from the bone and a fork slides in without much resistance.
Keep the braising liquid: That liquid is the base of your sauce. Spoon it over the shanks as-is, or strain it and reduce it on the stove for a stronger finish.
Make a thicker sauce: For a thicker sauce, strain 3 to 4 cups of the braising liquid into a small pot and simmer until it reduces and lightly coats a spoon. Add a few chopped dates while it reduces if you want it sweeter with more body.