Originally Posted by namretsud
One thing everyone is forgetting here is this is a 5.9 with ma's delightful keg. Do a quick check by removing the throttle body and taking a look down the passenger side of the back of the keg. If there is a pool of oil in there you have a vaccum leak caused by the fact ma put a steel plate on an aluminum manifold and with the differences in heating and cooling rates the gasket between moves and causes a leak, which in turn has been know to cause misfire codes. You can reseal it temperarily to get you by by removing the intake and using a new gasket or silicone gasket maker but the long term fix is the Hughe's repair kit that uses an aluminum plate. While you have the throttle body off it would be a good time to clean it with some carb cleaner or throttle body cleaner before replacing it.
OP you said you unplugged the O2 sensors but did you as one other poster said remove the precat sensor and tyewrap it out of the way so it doesn't bounce around and go for a drive. It will be noisy but if the engine runs better you will know that the cat is plugged because you have released some of the backpressure out the O2 sensor hole.
Did you replace the rotor when you did the cap?
I actually do remember hearing something about the gasket that your talking about but I guess I never thought to check, didn't think it would cause the backfires, severe hesitation ect. but I will check as soon as this storm passes ! no I did not even think to remove the sensor like that to relieve the pressure but that makes a lot of sense and I will try that as well when the storm passes. also with swaping the injectors around still no codes to tell me if the 3 injectors are the problem. I will check the intake and try the o2 removal as recommended and post with the outcome, thanks for your help !