IMO it might bee that you are trying to flavor too heavy a style of beer or you are not using enough, although 5lbs of cherries is a lot. Also, how long are you keeping the beer in secondary before bottling? A lot of flavors will naturally break down over time. For example, dry hopped beers will generally begin to lose the aroma and flavor at about 3 months. A lot of this comes down to your process, when you add the flavor and then when you bottle.