1995 Oldsmobile 88 Car dies while driving down road

Electrical problem
1995 Oldsmobile 88 6 cyl Two Wheel Drive Automatic

Additional information: The car was tuned up on 9/30/09-"Lube, oil & filter, transmission fluid change and power steering serviced". The problem stated below started occurring after the tune up. Could it be fuel injectors, spark plugs or spark plug wires?

My mother`s 1995 olds 88 just shuts off in middle of driving down road. Speedometer needle quickly goes over to 100mph (car does NOT accelerate that fast, fortunately)and then everything just shuts down. Power steering goes out. She has to glide over to side of road. It starts right back up and continues on. At first it was only doing this while she was driving slowly. Now it does it while driving fast, too. The mechanic that she`s taken it to four times now can`t find anything wrong. They have put in on computer several times and nothing shows up. They`ve driven it a lot and it never dies for them, naturally. Have you ever heard of this before?