Make sure the ingredients on your peanut butter just says "peanuts". Or "peanuts, salt". Although I'm not a big fan of peanut oil, since it's very high in omega-6 and you are probably getting way too much of that already. At least you're not using "vegetable" oil though.
Also coconut milk/cream is a very nice filler. It tastes REALLY fucking good, and is full of healthy fat.
Try flax seed meal instead of oats.
My favourite shake right now is whole milk + coconut milk + water + chocolate whey + golden flax seed meal, chasing a tablespoon of lemon fish oil