Looking at your pic, You could add an accurate thermometer or two closer to grill level. One closer to the firebox and another about 1/3 of the way from the stack. Both being 2-3 inches from the grill surface.
Weber WSM, Weber GA, Weber Spirit S-320
Charbroil Oilless Turkey Fryer
Wife LuzziAnn 1956 model.
Maverick ET-732, Superfast LSU Purple Thermapen, Party Q