Parasitic draw test for batteries on the truck?

Pretty much the same, though you may have more than 1 ground wire to the batteries depending on setup.

 

You'll need to remove the main ground from the batteries. Leave your jumpers hooked up between the batteries. But, you may not have just one ground. Depends on how the truck is setup.

A pic inside the battery box would help

 

Is your meter fused at 10A?

 

From my own personal experience those amp clamps aren't good for checking small amounts of amperage. They're meant to check high amperage circuits like the starter or alternator. They generally won't measure current in milliamps with any sort of accuracy.

 

Fluke meter is very accurate.I have an old one I bought years ago,still works great.Disconnect the ground cable and get the measurement between the terminal and the cable.Years ago you could start pulling fuses after that,find the circuit that was drawing the voltage or amps.New equipment has a lot more fuses and circuits so more difficult to find the source.