Where's your thermostat located in regards to the stove.
Fan speed is based on FEED Rate, the temp swing is probably too much and you don't give it enough time to catch up or your house heats up fast enough to satisfy the thermostat and the fans don't need to be put up to full. Mine will only run at full when I start getting up into the 80-95% Feed rate.
Check your FR (feed rate) to see what it is doing, the Fan rate is based on Feed Rate. If your Feed Rate is 50 or less, your fans probably won't be running full.
if the Blowers kick on/off full speed a couple times, that is normal (Look under the CoalTrol section V3 Features), also, you might be at the Threshold of the FR vs. CFT, it will do that sometimes ( This has been discussed in the CoalTrol Section too ).
We have all discussed the Temp. Setback and most of us don't use it, or only a couple degrees at a time.
Convection fanConvection Fan Start/Stop Cycling
V3 FeaturesV3 firmware features