Cooking techniques for venison neck

There are really two issues here. First is temperature, second is time, and they are somewhat inversely proportional to each other. Looking at AmazingRibs, one of my favorite online references, you can see some of the simplified data regarding both general information and elsewhere there are some venison specific cooking recommendations. The neck, in the second reference, due to the connective tissue is recommended to be cooked to a much higher temperature, similar to smoking a pork butt or brisket. So you either cook to a high internal temperature for a relatively short time (still many hours), or cook to a lower internal temperature for a very extended time.

Now, the issue is what cooking technique do you want to use? Smoking? I'd Traeger it at 225 until it hits 195-ish degrees like pulled pork. The meat itself will definitely be well done but the connective tissue will have broken down sufficiently. Sous vide? How about 135-140 degrees for 72 hours like short ribs?

From the food safety standpoint, cooking to less than 140 degrees requires much more care and preparation, and it does require you to understand a lot more about the potential risks in order to make an informed decision since you are the one putting the food into your mouth. Do I think everyone should cook sous vide? Absolutely not. You have to be willing to accept a certain degree of risk, or learn ways to mitigate that risk. In this particular case, unlike store-purchased meat the cut you have may or may not have unusual pathogens (parasites) that cooking (or freezing) techniques would have to account for.

I cook venison regularly since my family hunts. The neck is one of the most worked parts of the animal, so you need to cook it with an acid (vinegar, fruit juice), to break it down, an added fat to give it moisture, like butter or other animal fat, and with a cooking liquid of your choice (wine, stock, broth, etc) on low heat for a long time (1+ hour) so it doesn't seize. Be sure to keep it covered so no moisture escapes.
It still might end up grainy. Venison is one of the most unforgiving meats because of its delicacy and lean qualities. So, beginners often get grainy meat. I still get grainy meat sometimes!

Be sure you remove as much fascia as possible prior to cooking.

There's a reason people usually grind it up with a bunch of fat, though, so it wouldn't be bad if you did that, FYI. It will still taste good.