92 Honda Accord LX Transmission

The D4 Light stays lit up, as well as whatever gear you are in, so it'll have D4 and P light up if you're parked, and the transmission will start and stay in D3, it won't up/downshift, every once in a while it will shift, but goes right back. I replaces the TCU and it worked for about 10 minutes, then we changed the transmission fluid 3 times and ran it for 3 miles in between each change as recommended, it ran correctly for about 2 days and is now back to not working. I read to replace the VSS (Speed Sensor) but I'm trying to see if anyone else knows what's wrong before I waste anymore time or money on failed attempts.

You have a bad TCM (transmission control module). There's a capacitor on the the TCM circuit board that goes bad and you can change it yourself if you or someone you know is good with a soldering iron, otherwise pull it out and send it off to one of the rebuilders on ebay.