Yesterday I was driving my 1990 k5 on the highway. I had cruise on and suddenly the engine decelerated for a couple of seconds then resumed, then about a minute later it did the same thing. But this time the Service Engine Soon light came on. When I pulled into the nearest gas station, at idle and just above i noticed a rattle. I shut off the truck did my business came back fired it up and the light was out? But from then on in i have this rattle. TO me it sounds like it is coming from the bellhousing area or the back of the engine. I am totally perplexed on what it is and I don't want to break down either...Any help is much aprreciated....or ideas