Do you brown the meat first? That makes a lot of difference especially with pork. I don't like mushrooms in a slow cooker but each to their own. I sling a sachet of gravy mix in, tomato paste, soy sauce, whatever I fancy. The other things you can do is stir in a spoonful of sweet condiment at the end, redcurrant jelly, apple sauce (chunky) even maybe a little maple syrup; and about 20 minuted before serving, add small whole tomatoes to the top of the pot. They will cook in their skins but stay whole and add a lovely sharp note. The other nice thing is to add frozen chestnuts, either at the beginning to fall to bits and enrich the sauce or on the top for the last 20 to 30 mins to cook through but stay whole.