Looks like that clamp does DC voltage but not DC current. Many of us got the UNI-T UT210E. Discussion Here. Coupon and links here.
Obviously the fluke isn’t a bad meter, but the way they operate is to add tiny resistance to the circuit and measure the difference. DD and most of your drivers are very sensitive to this.
However, usually you only see those differences around and above 5amps, not 2-3amps. That’s why I asked about your leads, are they thick short pieces of wire, or are they still like 20-22awg with just a bunch of insulation to make them “heavy duty”? Even a cheap Harbor Freight meter should work fine under 4-5amps as long as you replace the leads with thick short wire.
And again, I don’t know much about the two batteries you are using, do you have any higher performance ones you can try? That could still be the issue too.