Since we are having the same Pgm problem I’ve just been out and checked mine for comparison. I’ve got 14.5v at tickover, lights on 14.2-14.3v and highbeam on 14v. I know you said the battery is new but if you fitted it new say last year and it’s been sitting unused it could have gone down.
I’d try connecting up a battery off something else that you know is good and seeing if you still get that drop.