Smoking at 225 Degrees

I am having some problems when smoking say briskets or pork shoulders at 225 degrees.  I have no problem maintaining the temperature, and I use the plate setter for the indirect heating.  I start the fire nice and slow and bring it up to temperature and get good steady heat and smoke.  It seems after maybe 3 or 4 hours the meat temperature really starts or maybe stops climbing.  I don't notice any smoke coming from the wood chunks in my egg.  I smoked a brisket today that was 6.5 pounds and after 10.5 hours the internal temp was only 164 degrees.  I opened the dampers more and took the daisy wheel off and got the temp up to 300 degrees.  The wood chunks started smoking really well again and finished off the brisket.  I had the bottom damper open around 1.5" and the daisy wheel open anywhere from 1/2-1/4.  It seems like the fire was just going out and retaining heat in the egg and not cooking the meat.  Anyone have any suggestions what i should do or am doing wrong?  Oh I use BGE natural lump charcoal.  Thanks.