2003 Mazda Protege... Chasing Transmission Trouble

[jsikes22]

I have an LX, engine starts and runs great, shifts smooth in and out of Drive, Reverse and Neutral. When driving after second gear it goes into neutral and then shifts back into second gear once RPMS are low enough. I have changed solenoids, checked wires for resistance, have a new PCM, and changed the Transmission speed sensor. Any help or advice would be appreciated!