Honda Repair: Transmission/electrical problem, speed sensors, 1993 honda accord

Question
I have a 1993 Honda Accord (automatic) that is giving me problems that  is transmission related. The D4 light flashes constantly and it isn't a code.  We have checked the fuses, rebuilt the transmission, replaced the TCU, and replaced the solenoids.  It is still flashing; when the car is drivin, it feels like it has two gears (1st and 3rd).  It takes off fine but once it time to change to second, it skips it and goes to 3rd and feels sluggish until it reaches the appropriate speeds for 3rd gear, and it doesn't change the 4th after that.  The only thing I haven't replaced are the speed sensors, but the speedometer works fine.   I believe it is electrical, but I don't know much about that when it comes to cars.

Answer
If the D4 light is flashing there is a code. The speed sensor can still be bad even though the speedometer is working. It sends two different feeds to the speedometer and the transmission. This is one of the possible solutions.
The next possibility is the "lock-up control solenoid". Either of these can cause this problem. Really the only other likely cause would be a wiring problem between the tranny and the tranny computer but this is unlikely.