Tcu?
 

The speedometer in my 2002 dodge neon recently quit working, and the transmission also quit shifting. I had the computer checked at the garage and they told me it was the output speed sensor. I had it replaced but it did not fix the problem. I never had any problems out of the transmission until the speedometer quit working. I've done some research online and I keep seeing transmission control module or transmission control unit. Could this be what is causing my problem? The speedometer randomly starts working for short periods of time and stops again. While it is working the car shifts fine.

I kinda had the same problem, but the speedometer kept fluctuating when I stepped on the gas. Or I maintain speed.
I will also get this revving sound as I would drive. My code was the tcu. And output sensor. What I did I just replaced the tcu and output and input senor. I changed my transmission oil and filter. The problem was resolved. This was on a 2004 neon 2.0