As to back pain, I spoke to this in an earlier post, but:

The Crossfire is "good posture" drive. You cannot comfortably slouch in the seat, you end up with back pains. You really need to keep the seat back fairly straight and slide your butt all the way to the back.

A couple tips to help make the transition...

Keep the seat bottom tipped forward as much as you can. This gives the sensation of sliding foreward out of the seat, forcing you to slide backwards to the seam of the bottom and seat-back.

Move the seat a little closer to the peddles. Again, this will force you to slide back further in the seat, sitting straighter.

Keep the back straight, or as nearly straight as you can handle. Tip of the headrest in line with the bottom of the seat back.

The point is to force yourself into a 90 degree sitting angle. Once you get comfortable with this you can start to progress the seat to a more natural position. But, never as slouchy as some other cars. I came from a Trans-Am, which is really as sloucher's dream. Especially compared to this car which can be like a German school marm cracking you with a switch every time you slouch.