Again, the only way we interpret evidence is through our perceptions.
In a godless universe our perceptions are no more reliable than the way an ant percieves the world. Only if there is objective truth can anything be said to be reliable.
Well, our perceptions evolved to give at least somewhat reliable information at the human scale.
Past that, you are correct, we have to be *very* careful. We *know* we are subject to optical illusions as well as illusions for other senses. We know our senses are limited in many ways (for example, we cannot detect radio waves without extra technological help). We know that we often misinterpret our perceptions.
And yes, there is still objective truth whether or not there is a deity.