1996 C3500 2WD, ~216,000 miles. Had trouble with running and starting - engine would "hiccup" while running, sometimes... and got to the point where it wouldn't start easily. If I managed to get it to start (which would require a jump start from my wife's car because it'd drain the batteries trying to start the truck by itself), it would run terribly for quite a while before gradually becoming smoother. Took it to the shop - first thing they said was "it needs a new injector pump". Probing further, I found that they have determined that the optical fuel temperature sensor is bad. I've heard about this "optical sensor" before. They say they can't change the sensor. I've heard that it is possible to change the sensor. Before I drop a four-figure sum of money on a 17-year-old truck with over 200,000 miles... tell me... can that sensor be changed? If yes, how much can I expect to pay for the sensor and about how long should it take a good mechanic to replace?