I've read this thread and the other that you started. From this info I'm convinced that your smoker runs a bit cool(averages about 230ish). Mine runs cool as well. I just crank my unit to 245-250 and leave it. I do not open the door and I NEVER foil. I also hardly ever drop my temps anywhere near 200 as it would take forever to get large meats done.
Both opening the door and the act of foiling(taking it out and wrapping) things will extend the cook by quite a bit. The moist environment of the cookshack just doesn't have a need for any foiling, period.
As far as I'm concerned foiling is to be done if you want one or both of these things done. To add or keep moisture in the meat and to speed the cook up with steam and a bit of pressure(wrapping adds a bit more pressure). If you absolutely insist on foiling then I would see about getting your unit to operate at a temp that's closer to a 250 average.
Also, as an electrical contractor I wouldn't be so certain you haven't got voltage drop even with #12 drop cord. Sometimes the recepticle itself is so far away from the panel box its already a bit low. The addition of a cord surely won't help.
My unit sure didn't like to be hooked up to a #12 cord on my outside recepticle. I wound up just plugging it straight and my temp swings went from 40 degrees to 25-30.
One more thing, but you may already know. You..will..never stop the temp swings. You can minimize them by packing the thing full of meat, but they'll be there. it's the natur of the beast since the thermostat is either on or off.
Hope you get satisfied in one way or another!
Oh...and WAY TO GO SMOKE! Big win at DEGA! Whooo!!! Sorry NC redneck came out a bit.