would a modulator valve and filter help my 1994 ford explorers transmission shift better than it does now?

The trans filter only filters oil. It has no effect on performance and unless there's a reason for trash to get in there, a filter change wont make any difference. The modulator, on the other hand, helps to determine the shifting point and line pressure inside the transmission depending upon the load on the engine. They used to make an adjustable vacuum modulator that you could stick an Allen wrench in the vacuum port and change the setting to cause a firmer or softer shift. Neither of these will fix slipping problems.

I agree with tracy However if your transmission is going out or slipping you can check transmission fluid to make sure you have adequate amount if that doesnt work then you are looking at a potential transmission repair meaning that the transmission must be replaced This is the 2nd most expensive to fix so you should determine if its worth to fix or get a new vehicle