I'm fed up!!!?

your coil pack is dying if you changed the plug the plug wire and the injector then the only other point on there is the coil pack where the plug wire connects too may be dying since you say there is nothing wrong sometimes and when your accelerating it gets worse(when theres more demand for spark) from what you tried and the milleage on the car id be willing to bet its a bad coil i havea 2002 3.8 camaro and a 2000 ws6 T/A coil pack failure isnt to common but it does happen as they get older