Depending on your dog food, that can be quite a few calories (in 2 1/2 cups a day). I feed BB LBP and it has around 450 calories a cup. I would decrease his feed by 1/4 cup a meal and increase some veggies like carrots or green beans to add bulk. Try weighing him monthly to see if he's maintaining, gaining or losing (slow but steadily) and go from there. Just my suggestion
(Right now my 6 month old is eating around 5 1/4- 5 1/2 cups a day...insane).