93 Honda Accord bad transmission with D4 light?

So I have a 93 Honda Accord LX with 288k miles and I'm starting to have an issue with the transmission. I know the car and especially tranny are old so I can expect problems, but this is my project car and I want to find what the transmission problem is before putting a new one in. Okay so the problem happens sometime, like 2-3 times a week, when I'm driving around for a while and come to a complete stop. When I try to take off from the stop the transmission would "slip" and the car will rev up to 2000 rpm and will feel like it lost power. If I keep stepping on it like that it will jerk and resume normal operation after like 5 seconds. When this happens at a stoplight I usually put it in D1 and it will take off normally and I will manually shift through all the gears with no problem. The D4 light also flashes constantly while driving when it happens. I want to know if this is a transmission control unit problem, torque converter problem, bad transmission in general or some other shift solenoid or sensor. I have put in Lucas stop slip and it helped for a month, but then started again. I also noticed the tranny fluid is really dirty and dark. Maybe a tranny fluid change with Lucas stop slip might help, what do you think?

Unless you own stock in Lucas, replace the tranny.

A flashing "N" or "D" shift indicator light means there's an electrical problem in the transmission control system. That is commonly a bad input or output speed sensor. Slipping usually means you need another transmission though. I'd take it to the dealer and have them give you an estimate to repair it. If you go to a transmission shop they will just sell you a rebuilt transmission and then call you up to let you know you have another issue.