Here is the battery drain test procedure out of the service manual. Basically what you are already doing, except making sure you don't break the electrical connection from the battery while hooking up the meter. This is out of the diesel manual but I don't see why it shouldn't apply to a gasser.

The thing to remember is that many of the computer modules stay powered for up to 30 minutes after the truck is turned off, or when the module is disconnected from power and reconnected. So if you just disconnect a battery terminal and hook in a meter, it could take 30 minutes for everything to go back to sleep.

When you get your meter hooked up properly, leave the hood up and the drivers door open so that you can get to the fuses. The battery saver relay will shut the lights off after a bit so you won't see that draw. Then if you're seeing more than 50 mA, pull fuses until it goes away.

Just remember that if you pull a fuse to a module that is asleep, when you put that fuse back in, that module is going to wake up and draw more current until it goes back to sleep again. So this test can be a pretty long, painstaking process.

And FYI, my truck pulls about 70mA for some reason. It might be the Edge Evolution programmer because it is always partially alive even when it's off. If I forget and leave my GPS on, it sucks down a fair bit of power.

But even at just 70mA, if I leave my truck sitting for more than two weeks, my batteries will be down enough where it'll crank pretty slow. I use a Battery Minder on my truck, I just put it on recently. I use it to keep the batteries alive while the truck sits and hopefully to put some life back in them, cause I think they're getting a little weak. I use this thing below, permanently mounted in the truck with the power cable coming out where the block heater comes out.

BatteryMINDer Model 2012: 12 Volt 2 Amp (12V 2A) Charger/Maintainer/Desulfator | ATV Battery Chargers | Battery Chargers by BatteryMINDers.com

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