I have no clue why you would have so much current going to/from your gas and water lines unless your power transformer (electric company) has a fault in it, or if you have some appliance(s) that have their neutral and ground wires swapped around.Sorry got those mixed up the 1.9 is going to the gas line,3.1 to water line.
The short 6' ground rods are used by cable TV techs. Electrical service grounds need to be the longer 8 1/2 foot copper-clad rods.Both ground rods are copper and about 5to 6 ft long. they are about a inch and a half apart, there so close they could of used one hand sledge to drive both in the ground at the same time.
AWG 4 wire is 0.2043" in diameter. It's pretty large.They are connected with what looks like a solid copper what I would say is a bendable rod, it doesn't look like wire unless it is a very heavy gauge.
What gauge wire did they replace the main power lines with?It was a licensed electrician that did the work. Since I have own the house there has been at least a dozen electricians, licensed, working on the problem. Two of them said they could not figure it out and just left, others have done some upgrade work like this last one, another said it was because of the size of the main power lines and replaced them from the meter to the panel.
AWG 2 is just over 1/4". AWG 0 is 0.325".
Just turn off the whole A/C and see if the current in the gas line goes away.I am not sure how to turn off just the air handler motor without turning off the whole a/c but I will give it a try.
Are you getting current readings on the ground wire(s) to/from the sub panel?The sub panel bus has all the bare grounds going to 1/2 of the bar and all the neutral lines to the other side, the neutral bus is pushed over to the other side of the panel from the ground bus, the neutral is the one hanging in the air.
I'm not crazy about the neutral bus flopping around. It should be anchored down somewhere, but unless you have a ground rod right there and tied in to the ground bus, the neutral bus should be electrically isolated from the ground bus.
Like I've said before, you should see little to zero current on the ground wires. If you're reading current in the ground wires, then there is a fault somewhere that needs to be corrected.