A burnt valve, it is not. When was the last time you changed your fuel filter? On the street, it should be changed every 10,000mi. You might seriously consider having your injecors flow balanced and blue printed. I would also, invest in some super high quality ignition wires with the setup you have, and not use the cheap **** that the majority of speedshops sell. I use a brand of wire called Magnecor.
www.magnecor.com For a fuel filter, I don't use an OEM fuel filter, but a Canton Racing "GM EFI filter #CM-15." It is compatible with the OEM style fuel lines and connectors. With what your describing, it sounds like it's definitely ignition related. I will also bet it's fuel system related, in one of the areas I talked about.