Very nice cook Bruce
I had same issue and as bosco had told me i had residue buildup on and around corners of back draft door so this wouldn't allow me to close it all the way even though i thought it was tight against
Once i cleaned both front and back draft doors this solved the issues and the no more red coals after i shut the grill down
It really amazed me not even a 16th of an inch would allow that and how little air flow is needed
My grill takes a long time to cool down once it is heat soaked but there should be no red coals after its extinguished