Glow plugs maybe?
On the 6.2L, they must be similar to the 6.5L and screw into the heads from the sides. 4 per side. Not much torque on them either.
You can pull the wire connector off the top of it and ohm it to ground. If it's open circuit, it's blown. If it reads something like a few ohms then it's ok.
Since they are on the sides of the engine, you might gain best access from the front wheel wells. Either that, or lean down in from the top through the dog house.
Are you having hard starting, so suspecting glow plugs? Is the Wait to Start light coming up on your dash, or no? I would check to verify that your glow plug relay is actually cycling properly. You should see 12V at the connector on the top of the glow plug while the Wait to Start light is illuminated.
Also, if you've used ether starting fluid on your 6.2L, this will destroy the glow plugs. Don't use starter fluid on them!