I am roasting on a Behmor 1600 plus. From what you describe your roasts do not sound slow and the temperatures you are measuring seem about right.
From what I understand (and I think this is the same on the 1600) there is a thermal sensor in the wall of the Behmor, which you can monitor with the 1600 plus, that goes to cooling once it has reached ~330F (~165C). This is not the temperature in the roasting chamber, but is obviously correlated.
This is my roasting process with approximate times and thermal sensor temperatures:
Preheat till the thermal sensor reaches ~250F (~121C)
P5 until temperature sensor reaches ~320F (~160C)
P4 until exhaust fan turns on (a physical rumbling occurs)
FC at ~11:00
Cooling cycle at ~12:30
I start the cooling cycle right at the end of first crack. I roast indoors and I do not want the chaff to get everywhere and I find the results to be fine. The roast will continue for a minute or so because I use this method, which is why I stop right at the end of first crack.
Hope this was helpful.