1995 ranger

i have a problem when i get on the highway and go around 55-60 or faster for a few miles my overdrive off light starts flashing any idea what causes this the truck has 158k on it thanks

get it to a shop quick. it means something is wrong in the transmition!!! mine did that and the valve body gasket broke loose and pluged up all the sensors and lines and fried the trans. $1800 to rebuild!!!

thanks i hope its cheep ;)