First of all who is telling you to do all this work and it does not fix the
problem, you need a " competent ' person to look at the car and determine
whether you have fuel and/or spark when this occurs, there a numerous
possibilities here and as you see guess work has cost you money. first of
all what engine is this?, then does this happen as you are slowing down, it
shudders and stalls, if you put it neutral and try to restart does it start
then when put in gear stall again?

It is hard to troubleshoot a problem when you are not precise about
pronouns. <g> When you say "it stops", do you mean the engine stops running
and you coast to a stop? Can you restart the engine in Neutral or Park? I
once had a problem with an 83 Cutlass Ciera 2.2 liter. Only after a long,
hot run, the engine would stall just as I decelerated to a stop. I could
restart the engine in P or N, but as soon as I shifted to any gear, the
engine stalled again before the transmission put any torque to the wheels.
It was so quick to stall as I shifted that the problem seemed to be
electrical or fuel, but it turned out to be a faulty solenoid clutch in the
transmission. My dealer gave me the impression that this was a common
problem for the Cieras, and the fix involved splitting open the trans.
Expensive, but it never gave me another problem after that.

BTW, find somebody else for advice other than the "fuel filter or catalytic
converter" guys.

Ed