Honda Speed Sensor...HELP ME PLEASE!?

I have a 1994 Honda Accord EX. The speedometer isn't staying correct and the automatic transmission is shifting weirdly. This is a very recent problem--less than a week--and the cruise control worked on the highway yesterday. The speed is usually pretty near accurate when at high speeds. It was suggested to replace the speed sensor, but I don't know for sure if that is the problem...someone also suggested the speedometer head or something. The D4 light has been blinking off and on since this has occurred. We have a fairly new transmission and we have kept it maintained. We had no issues like this before till we just got the radiator/heater hose replaced due to a leak.