I wont pretend to tell you I have the answer. But when you described your problem it sounded exactly like what happened to my Challenger years ago. The only main difference was that I was doing 95-100mph on the highway for an extended period of time (yes, I was driving like an idiot).

Anyway, car was driving fine at a nice click, when I lost power and heard a bang. I let off the throttle. Car was still running and heard nothing more. Gently got back in it and drove the other hour home from the Ozarks. When I got off the highway, I stopped to pick up a soda at the local fast food joint and noticed the car was making a rattle. Sounded like valve train. By the time I got home it was more noticable. The next morning I had trouble getting it restarted. I thought it was bad lifters so I changed them all. Still did not fix the issue, but it was at have the engine speeds as the motor sound. I was never happy with the motor after than and ended up having it rebuilt into my stroker. Still dont know what went wrong, but my piston skirts were all scored and I found the cam difficult to get out of the bore. Other than that, it is still a mystery. Ive heard of torque converter ballooning but dont know if that happened here.