On way home from work my engine shut down. I was driving along and suddenly I noticed a loss of power. My speed dropped from 60 down to 50 and then down all the way until the engine shut down. When I tried to restart it, it was hard to start. It finally started and then when I turned to go into my driveway it shut off again. I went to the station to fill up with fresh diesel and I put an entire bottle of redline in tank. The car started and ran fine for about 5 miles then it started to drop acceleration again. What is going on here. I don't see anything wrong when I look under the hood. The car has just had it's 100,000 mile service at my independent dealer and he changed all filters, oil, adjusted valves and all the things required in a 100,000 mile service. The car is a 1979 300cd with 102,000 miles on it. I did notice that since the service, I seem to have more power and the idle seems to be a little higher. I have had this car for 3 years and have had no problems until this incident. Please help as I am now afraid to drive this wonderful machine because I don't want to make matters worse. I start the car every day and let it idle for 30 minutes, but it doesn't seem to idle as quietly as usual after it reaches ambient temp. Thanks to all in advance.