Now here is a picture that you don't see everyday. The Sierra coughed and then died 5 seconds later while travellinng at 70 mph in the left lane! Fortunately, it was at a time and place where there were very few people on the road. I quickly coasted to the side of the road and stopped on the shoulder. It acted like I was out of fuel, but the guage showed more than half. I suspected fuel or electronics. The trouble with being alone is that you cant do much in the way of diagnostics. No cranking and checking spark or fuel....I reluctantly called for towing, and it took a while....thank goodness it was not as frigid cold as the prior week! It turned out to be the fuel pump, which is an expensive repair for an old vehicle. The good news is that it is guaranteed for life.