OK i had this exact problem with my 96 LS. I only i had a mis in cyl. 1 and 3. I went through all of the loops dist, injectors, spark, i was about to pull the head off and replace the gasket, but dad to the rescue helped me do a valve job on my car and since then the car has ran perfect. So i would get someone to do a valve adjustment on the entire head and see if that helps before spending any money...

JMAN