Hello and Welcome to the SMF Family. I see this is your first Post, please stop by Roll Call and introduce yourself. Please give us some info on you, your smoker, level of experience and your location.
" Never get done ", I guess I should have included, " in a timely manner or at all if the Smoker Temp is Lower than the desired finished Internal Temp (IT). " It's a matter of Food Science and Thermal Conductivity. The Lower the Smoker Temp the Longer the Cook. If you have a desired IT of 200*F and the Smoker is at 180*F-190*F, it will never get Done, as in to an IT of 200*F. Additionally if the Smoker temp is at 200*F it will get there but depending on Butt weight, Smoker efficiency, whether you Foil the meat and at what IT and how many times you peek, can very well take 3-4 Hours per pound to equalize with the Smoker Temp at 200*F. Generations of Chef's are taught that, On average the Oven/Smoker Temp should be set a minimum of 10% higher than the desired finished internal temp of the meat you are cooking to get done in a timely manner. It has been tested and proven by many of us here and within the Smoking community that at a Smoker Temp of 225*F, also the Min recommended Smoking Temp of the USDA for Safety, and with out Foiling or Opening the Door of a well ventilated Smoker, will take an average of 2 hours per pound to go from an IT of 40*F to 200*F. You can trim 30 minutes per pound with each Smoker temp increase of 25-50*F.
You said it took 18 hours for your meat to go from raw, 40*F to an IT180-200*F with the BGE at 180-200*F...Ok, How big a Butt? An average 8 Pounder?
Now it only takes 6 hours?...Same size Butts?...Same Smoker Temp?...THAT'S NOT POSSIBLE!!! Either the Butts are now the size of your Fist or the Thermometer you are measuring the Smoker Temp with is shot in the BGE and it is running a HELL of a lot Hotter than 180-200*F... For an average 8 pound Butt to go under 1 hour per pound your Smoker would have to be running around 350*F...JJ