That's pretty much how my PG500 acts at any setpoint below 300F. Whether it's normal or not, I don't know...
One thing I have started doing is setting my LHT and HHT at the same number. It requires a bit more maintenance but slightly reduces the temp swings. I just have to tweak it every hour or so as ambient conditions change.
I will say though that even with all that heavy smoke, it has never had an ill effect on my cooks. I have never had an acrid/bitter oversmoked flavor even on briskets and pork shoulders that cook 12-20 hours.