Update:

Since I last posted I found out that this engine had been recently pulled out to replace the oil pan. The guy that did the oil pan did such a poor job that the pan gasket fell into the bottom of the oil pan when he re-installed the pan. This guy apparently didn't even notice that the gasket was not in place. The truck was then taken to a shop and the mechanics there were able to lower the pan enough to retrieve the gasket and install it correctly.

Because of the bad work done by the 1st "mechanic" I started looking around the engine and found several problems that I was able to repair. I repaired 5 pinched and skinned wires as well as 1 broken wire in the harness that goes across the engine just under the hood. I also found 3 of the 4 battery connections were corroded/loose. The medium size copper stud on the starter solenoid had been stripped which left the connection loose and unreliable. I was able to chase the threads and install a lock nut to hold the starter wire in place. I found that one of the ground straps had been frayed and the radiator reservoir wasn't installed properly.

I have a feeling that more things will show up in the future or upon closer inspection of the engine.

The truck hasn't been driven much since I repaired the electrical problems so I don't know whether or not the problem has been resolved.

I finally got a chance to ohm the valve cover plugs yesterday. The injectors all tested around 3.6 ohms. There was 1 glow plug on the passenger side and 2 on the drivers side that failed.

Any thoughts?
Does the failed glow plug test mean that I need to remove the covers and check the plugs and harnesses or dose is simply mean that there are 3 bad glow plugs?
Is it possible the electrical problems that I found were the cause of the rough idle, shaking and loss of power?

Thanks in advance for your help