There are several factors for consideration, first would be water temperture, if the water temp is down at the time it will show the stack temp down a bit as well. second, would be the fire and where it is in it's burn cycle, early on in the burn cycle, the stack temp will be down because the fire and brick are not as hot as at the end of the cycle. Third would be wood quality and how much gas you are producing, one thing I notice about wood quality is that I prefer more dense woods with some moisture in the wood over very dry or partially punky woods, really dry or punky woods will flash off very quickly whereas dense woods with some moisture tend to give off their gasses slower and more steady. Your stove will burn about anything for clean wood and give you heat but there are lots of variables that you will learn to identify.
All this being said, I would say it's about time to brush her out and don't forget to take a look at the air box while you are cleaning. How do you feel about the stove's performance at this point Cabo?