Greetings! You need to get more time on the unit burning at different rates. Certainly slow dow the feed rate IF black coal is coming off the stoker plate.
However, you still need to learn the characteristics of the Reading stoker before panicking. There is a learning curve with each appliance, and you have started from square one.
Open the door several times a day to look at the length of 'dead coal' getting ready to drop off the stoker plate. You should not be sending any unburnt coal to the ash bucket.
The coal you have might have some shale or crap in it, so if you think of it, lay out some ash and photograph it for us to look at. Good luck and allow each adjustment several hours before you jump on it.