1990 buick lasabre-no spark

I have a 1990 buick lasabre custom,3.8 liter. The pprioblem is that it dies every so often,im driving along on day she shuts off,no warning.I have change 4 ignition coils and modules because garages said they were gone, new crank sensor,new plugs.removed and cleaned all ground wires, another garage said not grounding,.On the last ignition coil and module car was not working for 2 weeks then one day she started again,so i put the old modules back on that garages said were gone all working,then 2 weeks later going up hill car shuts off agin, no spark at all in wires,now same prob car just turnes over,getting plenty fuel,battery good,just no spark,it just comes and goes.When car is working it runs excellent,then bang agin no spark.Can anybody help,please,this has been going on for months all kinds o suggestions,no luck.Any help would be appreciated