my engine stall in the hiway , I check spark plugs etc, what could it be? on 1991 Saab 900

when I drove the car in town, or when I go on the hiway the engine loose power and speedometer go back, it dosen't do this very enough, but when it happen, Ipull the car from the road and the cut off. and when start the engine the problem is gone, until next time

Asked by for the 1991 Saab 900
I would check your fuel filter. It needs to be changed every 30k or 3 yrs.