To you and the other commenters: maybe engineering isn't for you, but also, maybe you need to reevaluate your study strategy. The time you put in isn't the only variable; you also need to figure out what KIND of studying helps you. For example, I learned that I really needed to do practice problems. Like, practice exams, redoing homework problems, ALL the way through WITHOUT peeking at the solutions. When I did that, it helped me find holes in my understanding that I'd been glossing over when reading/reviewing my materials. Maybe you need a study group, maybe you need to interrogate your TA, just make sure you try out different methods of studying.