A real FICM check begins with a test of the batteries.
Take them out of the truck and run them down to an autoparts store. Have them load test them (free service, if it isn't find another store).
Replace the batteries as a set if either of them test as marginal or fails.
When you return home, place the batteries on a charger and charge them to 100%. Even if you bought new batteries, charge them since they don't come off the shelf with a full charge.
Clean/check the connectors (This is where I found my problem), reinstall, get your multi meter, then CLICK HERE
for written directions on how/when to check FICM voltage readings.
If you see less than 46 volts during the testing, your FICM needs to be repaired. Check out ficmrepair.com if you need to have it repaired.
The reason for addressing the batteries prior to checking the FICM is that the way these trucks are wired, they will crank over rapidly, yet the batteries may not have enough "juice" to fire it up. The weak batteries can also kill your FICM (among causing other electronic issues).