Volvo: 1993 Volvo 850 Stalls, volvo 850 glt, faulty sensor

Question
Hi! I drive a 1993 Volvo 850 GLT automatic car. The problem is, I will be going 50mph or even just sitting at a stop light and it will completely stall out. When I say stall, I mean it shakes, all lights flash off, and I lose power steering. The car has been flushed clean, new wires, spark plugs and fuel pump. The battery is good according to the machine, and I do not know what else to do. I have taken it to 3 shops, and still nothing. Please Help!

Answer
This seems to be a common problem for the early 90's era Volvos.  The bad part is, it's hard as anything to diagnose such problems from behind my computer.  I can only speculate.  That said, my limited experience has shown that this is usually due to a faulty sensor.  Did any of the 3 shops check the car's computer for codes?  A computer is really the only thing that could tell you which sensor, if it turns out to be a faulty sensor.  I doubt anything mechanical would cause such problems, unless it was your cooling system, but I would think that at least 1 of 3 shops would have checked that.  If not, keep an eye on your dash thermometer.  If your engine is warm but your thermo hasn't moved, you might have a bad thermostat.  
JD