I've had the code reader lie to me about the correct cylinder before. It may be other than #5.

 

Do a power balance test. Let the engine get fully warm, disable IAC, (just unplug it.) and unplug the coil for each cylinder, one at a time. If you have a cylinder where there isn't much of a difference in idle speed when you unplug it, there is your problem child.

 

So over the past few weeks I have swapped around fuel injectors, ignition coils, and spark plugs. Reset the engine codes multiple times, and checked for any leaky vacuum lines. Nothing seems to be changing the confirmed cylinder 5 misfire, and detected cylinders 3 and 4 misfires. I was unable to do a compression check, the spark plug adapter piece was too large, and wouldn't allow a socket into the hole in the engine block.

At this point, if I drive more than 5-10 miles my check engine light begins to flash. Really in desperate need of a way to troubleshoot and fix this issue.

 

Are you losing any coolant? Back when I had an head gasket issue, it was with cylinder 5. When I pulled the plugs, I could see that #5 was being steam cleaned and with a bore scope, I was able to see a little coolant in the cylinder. This truck always starts on first crank, but when it was manifesting, it was cranking longer before starting.

 

The answer to the coolant question is yes, but a strange yes. It's not that the coolant leaks and is lost or burnt up. For some reason my coolant all gets pushed back into the radiator reservior about once a week due to excessive pressure in the coolant system. I have to manually pull the coolant out of the reservior and put it back directly into the radiator cap, on a regular basis. If I keep putting in new coolant, the reservior overflows and makes quite a mess inside my engine bay.

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Unplug the front O2 sensor(s), and go for a drive, see if your miss is gone. Also, verify you have correct fuel pressure.

 

Could a faulty O2 sensor throw off the fuel/air ratio in the cylinders enough to cause a constant misfire, while at the same time no throwing a code for the O2 sensor?
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Yes.

O2 sensors have a variety of failure modes that won't set codes. So long as the data the PCM is getting from the sensor is within the 'acceptable range', the PCM will use it. It has no clue if the data is accurate or not.

 

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I'll try this after work tonight and get back with the results.

 

That might be your radiator cap malfunctioning. When the pressure drops in the radiator, a valve in the cap should open and allow reverse flow back into rad. On the topic of HG, try starting the truck cold with the rad cap off. If the coolant becomes turbulent in the neck, or shoots out, you've got a HG issue. You can also rent a block tester to sniff coolant for gases.