Hey Mike -
Are you using DVI or some sort of bulk or mother starter? I used to have extremely long drops in pH due to using dry culture, and had to play with that because I make alpine cheeses exclusively, and with tommes, I had to manage a slow acid curve while trying to keep floc times reasonable (I use a multplier, not a clean break method).
I can't find more than a few logs as it's been many years away for me, but I seem to recall some at times ridiculous periods to any pH drop and as well, floc times - easily well over an hour or more. I just tried to tweak the culture for change in pH (also, it can be almost nothing, as they are replicating, then a really quick drop as they go to work), and to get the floc time to within a 12-15 min. window.
Are you certain of the freshness of your rennet? Using cold water? Sprinkling it in quickly once you've diluted it?
Just saw your edit on the CaCl concentration. I'm used to around 30-33%. Unfortunately I think linuxboy, Francois, not sure on Sailor aren't around any longer as they were my science gurus but I don't know why free calcium would have an inverse effect like that on floc time (I have her book, though, and am going to see). Interesting.
Anyway, the short thought is to make sure you're getting acid production, make sure you're using fresh rennet, diluted in cold water (I used to put my beaker of dilution water in the freezer, while doing other things), and adding the rennet as quickly as possible.
Hope this was helpful. Sorry for the length.