Do you have any aftermaket fuel pressure enhancing box on your truck? i.e. Egde EZ, Diablo Power puck, etc...? This aggrivates the problem with internal injector leaks. They are known for pushing out the small check ball on the side of the injector body causing fuel to spray into the crankcase. If you are not afraid of making a mess, you can take the valvecover off with it running and unplug the fuel contol actuator. It will raise the fuel pressure to max and you will be able to find your problem if it has one. It will steam and spray around the body of the problem child injector. Be careful though, and stand back from the engine and do NOT lean over the top of the engine while doing this.