It sounds to me like you put WAY too many lit coals on, based on what you wrote.
Have you read up on the "Minion Method." You should be starting with something like 90-percent unlit coals, and 10-percent lit coals. Raising the temperature is far easier than lowering it.
I have an 18.5 WSM, and start off with just under half a chimney of lit coals on an almost full ring of coals and wood chunks.
Seriously, if the fire is too hot, you most likely started too hot, and cooling the fire down is not easy. Always err on the too cool side, because that is easier to fix.