random cutting out
 

i have a 1994 fd it starts and idols fine but when i put my foot down it wont go over 60mph i have tried in different gears and still dies at 60. it also does it sometimes if i give the car full throtal befor 60mph but if i gradualy build the revs it will rev to about 8500 but then dies again at 60mph. i have changed the plugs and fuel filter and done an oil and filter change but it hasnt changed anything. does anybody have any thoughts.
thanks in advance for any help.