They almost ALL go through that Stall Zone!!!! Actually, I never had one that didn't.
Next time you get it to 160, cover it with foil. Make sure there is a little mopisture in there with it. It will ZOOM right on up to 200.
Or, you can do that AND crank the heat just a little.
Try a Hot nad Fast one sometime. Get your smoker to 375, cover with foil at 160 and take it off at 200. You will have Pulled Port Sammies in under 6 hours guaranteed!!!!!!