2005 Dodge Neon I have only first gear.

I bought the car used and it ran/drove fine on a short test drive. On the way to work the first day the CEL came on and the code was for having the wrong key so I let it ride. After driving it to work and back for three days it was still shifting fine. The fourth morning, as I turned onto a side road and pressed on the accelerator it was as if I had thrown the shifter into neutral. There was a rattling noise from under the hood when I raised the rpms but no reaction from the transmission. I coasted to the shoulder and moved the shifter through all gears and still nothing. I then put the lever in park and shut off the engine. When I restarted the engine and selected Drive the car took off as normal until it reached the speed necessary to shift into second gear. Again it was as though it went into neutral. I assumed it was in limp mode so I drove it in first gear the rest of the way to work, keeping the rpms around 2000.

That afternoon I limped it a couple miles to AutoZone to have them pull the codes. The only one I remember right now is P0700 and it still had the one for the key issue. I have replaced both the input and output transmission speed sensors as well as the shift solenoid pack. I've replaced the fluid and filter as well. The fluid was quite dark and slightly burnt smelling. There were a lot of metal flakes on the output sensor as well as in the pan. I still have only first gear working. Any ideas?