Remove the NEGATIVE battery cable from the battery post. Take a test light and put one end of it on the now bare battery post and the other end on the now loose negative battery cable end. If the test light lights you have a current draw.

When doing the test make sure everything inside the truck is turned off and the doors closed. If you have a working underhood light, you will have to remove the bulb or else close the hood far enough to where the light would normally turn off.