Lagging meters can often be caused by the hold down screws being over tightened. Loosen them a bit and see if it helps. Is the meter pointer dragging across the meter face? Sometimes the meter movement is just dirty and this causes the meters to act sluggish, they are over 50 years old.
Some folks on this site are talented enough to disassemble, clean, and reassemble these meters. They do it because there are no replacements.