A fairly old question by a left user but since I know many people who have this exact problem I decided to answer this.
Well, Allah makes all sorts of creatures but the responsibility correlates with the degree of our God-given talents.
Allah does not charge a soul except with that within its capacity
But as for this particular problem, I have seen people who have a good knowledge of Islam and do their best to adhere to Islamic rules and values, but there's no passion and emotion involved in their religious observance and life.
My understanding is that if the intellectual requisites for a lively religious practice (knowledge and faith) are really there, then the only source to look for problem would be lifestyle and psychological health.
So I would recommend reading three of my answers that I have written on psychology-related problems for religious observance where I make many notes on importance of mental health and life-style balance.
Then, as I have explained sins of all sort impact our physiological and psychological health. The impact by majors sins can be adverse and long-lasting. Now given the OP's agnostic background this might be a responsible factor unless it is really due to genetic makeup that they suspect. Now depending on the nature of the sin there can be specific remedies. The spiritual remedy, i.e. repentance is common to all but it is meant to eliminate the desire for sin in our being and inspire us to make up for the past, not directly addressing psychological and even physiological conditions caused by sin in our being. Therefore for specific remedies we need specific knowledge of the person, his life and health record.
Now since the OP has specifically suspected to have psychopathic traits and suggested it to be from his/her genetic makeup, there are bad and good news. Modern medicine doesn't reportedly have effective treatments for psychopathy. But then it has been recently proven that our genes change during our life. So we can say if a psychopathy case has genetic causes, there are chances that it can change and improve.
Further good-news though comes from my knowledge of the traditional humoral medicine, widely practiced today as an alternative medicine in my country. Based on the principles of the tradition Greek-Iranian humoral medicine, psychopathy can be explained in terms of black bile or yellow bile dominance in the entire bodily complexion or the brain.
For each complexion and humor dominance there are physical and psychological signs in humans. Both black bile and yellow bile dominance are associated with skinny and dry looks. They are also associated with a very poor emotional life. This artistic depiction can give an idea of the general physical and psychological traits of the four typical complexions. The yellow and black bile complexion are the two men on the right even though the yellow complexion guy (the upper right) is depicted as more dry than skinny which detracts from an archetypal yellow bile.
Yellow bile dominant individuals though are more likely to display psychopathic traits, with black bile individuals being quite the opposite: they tend to be submissive and meek but still having little emotions.
But like I said, there can be that the dominance only affects a certain organ of the body, here, the brain in which case the physical signs associated with general complexions would be absent.
In either cases, apart from life-style recommendations of an emotionally and spiritually balanced lifestyle (see my second linked answer), medial treatments include dietary reforms and central to that would be a substantial increase in one's routine fruit intake, specially sweet watery fruits like apples, grapes and carrot juice.
This type of food help with improved blood production and circulation in the body which positively enhance both mental functioning and emotional vibrancy.
So by knowledge of human nature, we can treat even many of the negative traits that we attribute to our inherited build or genetics and not think we are condemned to some "inherent" traits.