A few thoughts:
- Not the dad. Not the mom. Not your job.
- Newly married. Focus on the marriage, don't go slinging mud at the exes.
- You have the hallmarks of a fixer. Are you, perhaps, an engineer? All this new "I want to be an engineer" from the kid may be nothing more than an attempt to win your approval.
- Junior year is too late to become an awesome engineer on a traditional track. Let it go.
- Ask him what he'd like to accomplish by the end of his junior year. Specifically. I have a junior-they don't think five years down the line and big sky kind of stuff.
- A crap math track won't slow a kid who's amazing at math that much. If he's doing crappily on a crappy track, it may not be the mom you want to throw under the bus. It may not be his thing.
- See number 5. Ask him. Follow his lead. Don't try to fix him, for the love of god. He's fine just like he is, and any whiff of you suggesting he needs to be "improved" is going to torpedo your marriage and your relationship with this kid.
- See number 7.
Seriously, man. Support him; don’t fix him.