I've heard the claim that rational ethical theories do not require God or any other deity in order to arrive at their conclusions. Pure reason is enough to provide sound ethical arguments. However, when I look at theories like Utilitarianism, I can't help but ask how happiness or pleasure is, ultimately, defined through those approaches. You can always keep asking why does action A lead to happiness, and why is happiness defined in that way? In the end, I'm not sure how pure reason alone can lead to a grounded ethical framework.
Whether or not you think pure reason alone can lead to a grounded ethical frame would be dependent on how idealistic a view you take on ethics. You should also ask yourself what you think it means for an ethical statement to be grounded. Can something only be grounded if it comes from god? Or does it just need to be a part of an agreed upon code of ethics?
Taking into account not only your skepticism of utilitarianism, but also my global skepticism towards any ethical theory claiming itself to be ultimate; I think as long as we're rational thinkers we will find problems with any doctrine which is dogmatic in process.