Hi Don,
I'm fairly new to the 008, but I've used it a lot more than you have in the short time I've had it, so I'll pass along my limited experience.
I've never fixed hamburgers in mine, since I've been very happy with the results I get from my grill on those, so my experience is mostly with larger cuts, such as butt's, picnics and briskets. I may have to try it now though.
Your description sounds pretty normal to me. Keep in mind that there are a lot of variations.
1. Doing the initial seasoning/break-in I put a pan of water on the middle shelf, like the instructions state, in order to stabilize the temp. At 200 deg. it varied from 173 to 228, so averaged out at the 200 deg. Before someone jumps in, do not use the water pan after the first seasoning smoke and better yet, search the forum for the best way to season your smoker.
If I check it with the smoker empty, the temp. variations are again different. The higher temp. gets higher when the smoker is empty. It varies approximately 30 degrees from lower shelf to top shelf, and gets hotter toward the front than the back. Your wood will usually burn more completely at the front of the wood box than the back. From what I've read, most people have pretty much the same experience.
2. Since then, it has varied differently, depending on how much meat and what cut of meat I use. It seems to do better with more and larger cuts of meat.
3. When first started, my 008 will initially get close to the set temp. then go back down, but remains above the temp. of the meat. As the meat heats up, the 008's temp continues to vary, but the high and low temp. increases as the meat temp. increases and the low temp always increases to stay above the meat temp. I start and do most of my smoking at 225 and I don't think it has ever reached the high temp during a smoke. It comes pretty close as the meat comes up to it's finished temp. (About 190-205 for butts, picnics and brisket.)
4. This may be the most important point I can pass on. I've learned that monitoring and worrying about the smokers internal temp. during each smoke is a waste of my time and not worth the toll on my mental and physical health, since the finished product has never been anything but outstanding. Everything I've cooked has been tender, juicy and much better than anything I've ever fixed in my kitchen oven. This is difficult for me to say, since I'm somewhat O/C and worrying about all of this stuff just makes my day.
As long as the lower temp continues to stay above the meat temp. I know it's going to come out great, whether, or not the higher temp. ever comes up to the set temp.
5. I now consider this normal, but please do call Cookshack's customer support and talk to them.
I hope this helps a little and maybe someone with more experience will jump in and contradict me. Again, call their CS, I did to ask about the variation during my seasoning smoke and they're great to talk to and very helpful.
By the way, how did the burgers come out?
Pat