I drove my truck about 6 miles to work today and it started spitten and sputtering going down the road. i had to keep down shifting and push the clutch in to see if it would quit. i t did it like 5 to 8 times and it dididnt start doing it until i was about half way to work. any suggestions on what to do would be great. it is a 1988 ford ranger extended cab XLT 2.9L V6 fuel injected.