98 explorer sohc 4.0 4x4 my overdrive light will flash when it doesnt go into overdrive right away it will stay in third for alittle bit longer then it sould if i let it sit for a few hours it will reset its self untill it does it again what does this mean

 

You may have had this checked already, but it means you have a transmission code in the PCM. It could be anything from a gear rati error to a sensor of some sort. When the OD light flashes it will dissable lockup and OD and will make the trans shift hard. Just need to get it scanned and see what it is.