any suggestions on marinade? should i inject it?

Here is the way I cook all shoulder I dont bone out.

Make a bag out of heavy duty foil.

Season the shoulder with your choice of rubs. Put on pit and cook for an hour or 2 and get a good crust on it.

Place in foil bag and pour in 1 bottle of a good Italian salad dressing. Fold the open end up and be sure the bag is leak proof. No leaks for steam to escape thru.

Put on pit or in oven at 250-300 for a couple more hours.

The bone will be on top of the meat and the meat will be tender and tasty.

I have cooked 4-6 at a time for my crews in the past. They loved it.

hamburger or chili meat

Just spice and cook on lower heat in the oven for a longer time..Tastes just fine and becomes mighty tender too.

Yesterday I cooked a venison ham roast in the crock pot and members of my wife's family who do not like venison, LOVED it.

Recipe from my BIL and incredibly simple - pour 1 can of Coke into the crock pot, cover the top of the meat with BBQ sauce and cook on low in the crock pot 8-10 hours. I threw it in yesterday morning and when I got home, it was done, tender and GOOD.

Coke and BBQ sauce is all you put? I think i will try it tomorrow

I also slow cook mine all day in the crockpot. I let it sit over night in a blend of one cup water and italian dressing mix, ranch dressing mix, and two packages of brown gravy mix. Add in potatoes, mushrooms, carrots, pearl onions, etc about 1/2 way through.

By dinner time it's fall off the bone tender and has a nice gravy that it's simmered in all day. Good stuff.