country road,
If you are concerned about tenderness, use a tenderizing mallet to achieve the right texture of your meat..Marinating should be done for taste, not texture..
Venison Roast Recipe :)
Ingredients :)
1 venison chuck roast,
1 small onion, chopped,
1 tsp. chopped garlic,
2 sprigs fresh tarragon,
1 tsp. freshly ground black pepper,
1/4 cup red wine,
1/4 cup soy sauce,
5 whole cloves,
6 slices pancetta (non-smoked Italian bacon)..

Combine all the ingredients, except the venison roast, in a big ziplock bag and refrigerate for at least half a day to marinate..Remove the venison roast from the marinade and put it in a baking dish, cover it evenly with the pancetta and place it in a preheated oven at 475 F. Roast for 15 minutes, cover with aluminum foil and lower the temperature to 350 F. Roast covered for about half hour or until the desired doneness. Remove the foil for the last 5 minutes of roasting. Remove the venison roast from the baking dish and keep it warm for 10-15 minutes before slicing. Add the preserved marinade to the baking dish and scrape the bottom to loosen and bits of flavour that have stuck to it. Strain the liquid juices from the dish in a pan and bring to a boil. Reduce the sauce slightly and pour it on top of the venison roast after slicing...
Good Luck and I hope this Recipe suffice your desire for Venison Roast!!!

I would put it in a crock pot and let it go all day. You can add any of your favorite veggies. If you want a good marinade try McCormick grill mates.

Country,

I've found chemical meat tenderizers to leave venison mushy, a texture I don't care for.

Aging will certainly help with tenderness. Never cut up a carcass while it is in rigor, the rigor will stay with the meat and you will be stuck with a pliable product!

Check out Eileen Clark's recent cook book, "A Slice of the Wild." She is the wife of noted writer John Barsness. you can purchase the book from their web site. I've not fond a bad recipe in it. She also address tenderness issues and supplies recipes to deal with said pliability.

http://www.riflesandrecipes.com/

Three days is cutting it pretty close, this particular deer might have still been in rigor(to one degree or another). There are multiple factors that can influence when the carcass starts coming out of rigor, such as- temperature, animal size, environment, etc.
You might think about letting them rest on ice for 4 or 5 days at a minimum, in order to eliminate the chance that you might be processing meat that is still in rigor(like what Bee said). As long as you drain the ice chest and recover the meat with ice every day you will be fine. The main goal is to keep the meat under 50 degrees fahrenheit, and this method(properly maintained) will easily accomplish that.

Another method to consider would be using an extra fridge. Set the thermostat to hold around 36-45 degrees. Quarter or bone the game and place it in plastic totes and place in the fridge. Close the fridge and do not open more than once daily to check the temperature of the meat. This would reduce chances of contamination and having to continually buy ice. Just as important, clean the fridge/totes and disinfect after every use.

These are just suggestions/examples of methods I personally have used. I am by no means an "expert" in such matters, but my job is directly involved with the meat industry.