1. make sure that all the stove pipe joints are tight we want no room air going in the chimney.
2. make sure the pipe is in the chimney flush with the tile and that it is cemented in, we want no room air going in to the chimney.
3. look at your clean out door if their are any air leaks, check it with a match run it around any gaps or cracks if it sucks it in duct tape it shut.
4. if you can build hotter samller fires avoid loading it up and closing down the air.
5. If you put your stove therm on the stove pipe 1' away from the flue collar you should have 350 to 500 deg. at this temp. your chimney should stay hot enough to prevent the build up.
6. creasote will condense on the surface if is below 250 deg. The goal is to keep the chimney hot hotter is better
Is most of your build up at the top of your chimney???
Rich