Honestly, I wouldn't worry about it.
Answer these questions:
Do you always have to keep the truck plugged in to get it started?
Do you have to cycle the glow plugs multiple times?
Does the truck use oil? How much?
Now, to answer your question about compression:
Pull the valve covers
REMOVE ALL OIL FROM AROUND GLOW PLUGS.
Remove all glow plugs (DO NOT LET OIL INTO THE CYLINDER. This will alter the results.)
Install Compression Tester Adapter into glow plug hole. Make sure you thread it in correctly, and by hand only.
Attach the compression gauge.
Now, either unplug the CPS and have someone crank the engine while you monitor the gauge, or just remove the top wire from the starter solenoid and use a jumper wire from that post to the positive battery terminal. This will turn the engine over, but not start the truck.
Compression should be in the 380-415psi range. Even at 360psi, the truck will run. I wouldn't want to see more than 10-15% difference between cylinders...
Best Car & Motorcycle Insurance | Auto/Moto Protection Today | FREE Trade-In Quote