So am I understanding correctly that each one of the leads going to the block all draw 4 amps or regardless of which one you connect the power draw appears? it's not one single wire you were able to isolate as where the draw is coming off from?
for a ground issue, a quick and dirty way to check is to use a set of jumper cables. connect both on one end to the engine block, then on the other end find a good place on the frame and to the negative battery cable. then do the test again.
I am not too familiar with doing the test with a multi-meter as much as using a test light and watching the bulb brightness. a dim bulb will be the keep alive memory for the radio and the PCM, but a bright bulb is a draw.
in doing the test, eliminate the easy stuff first. pull the hot lead and small connector off from your alternator, wrap the lead with a rag or something to prevent it from touching anything. make sure everything in the cab is off and the doors are closed. also in the dash fuse panel, pull the fuse for the radio. this will take the radio and alternator completely out of the equation. then re-test.
Questions: does your truck have an aftermarket radio, amp, or alarm installed? Or any other non factory add-ons like driving lights, LED bulbs anywhere. or from factory some models had dome lights that stayed on for a minute or two after shutdown and parking.
After isolating the mentioned above and the draw persists, then it's time to re-connect the battery and go though the truck looking for and making a mental note on what works and doesn't. Domes, cigar plugs, any interior and exterior lights, ect...
going back to testing and begin pulling fuses one by one until you ether have no more fuses to pull or the draw goes to nothing. Note, use your phone taking a photo of the fuse box layout and what size fuses are in each slot so you can put them back. There is also a fuse in a water tight cover next to the junction block on the firewall for the fuel pump.
at one point you should find which circuit the draw is on.
If when all fuses are pulled from the box and the draw still persists, this is when you get crazy with disconnecting other things like the trans main connector, PCM behind the glove box, turn signal harness under the steering column, ect...
If all mentioned above is disconnected and the draw persists, then you have a wiring issue somewhere in the truck and the "fun" begins....