Ok, my LS is finally fixed. The problem was the coil on the drivers side. This was suggested by many people and is written about in many postings on this site. It seems my mechanic may not have tested the coils thoroughly, as he said. After I brought him a printout of the suggestions in this posting string, he went back and looked at the coils again. So I have new parts, that I believe I did need, fuel filter, cat, spark plugs and he only charged me for 4 hours of labor, after the car was there for 1 week, but I still think I will look for a new mechanic.
Thanks to everyone that contributed to my posting. This is a great website.