Yeah but after ANH he knows that Anakin is Luke's father and a Jedi, and he's pretty sure that Palpatine's a bad person. Let's just say in a variation of a plot bunny Ish adopted and turned into a fantastic epic with what's looks to be an even more fantastic sequel, that Han had been sent to assinate Vader and/or Palpatine. Now I don't think very many people give Han enough credit for his intelligence. He had to have some above average level of intellegence to be admitted into the Imperial navy for fate's sake. Maybe if he overhears a conversation between Anakin and Palps, he starts putting things together. Now where he goes from there after he figures out Anakin = Vader is anyone's guess, but I think that he would have figured out Anakin + Palps = at least Danger in some way shape or form.