Hey grillin_all_day, looks like I'm using about the same size splits as you are in my Wrangler. But, I think you just told me my problem whenever I add a stick of wood. When you say "...throw one of those on, leave the door open for about 5-10 mins..." that's what I haven't been doing. I always leave my exhaust wide open. But, when I add a stick of wood, I've been adding it from the top (keep that firebox grate out) and maybe leave it open for a minute, as most of the time my splits start burning quickly. And, I adjust my air input by opening it a little. But, every time I either get it too hot for 10-15 minutes, or I get white smoke for 10 minutes or so. It may not be that long...but I'm a perfectionist, and it sure seems that long before it stabilizes again. :-) Now, when you say "leave the door open" are you talking about the top door to the firebox? Or, are you talking about the end door where the inlet vent is? Either way, sounds like I'm not leaving mine open long enough when I add a stick.
Talking about doors, brings up another question: Is your nut holding your intake damper vent too loose? Mine is entirely too loose, and it's hard to get the vent to stay in the same position I want it. The problem is the dang nut is welded on to the bolt. I need to cut it off and put my own bolt and nut on there, so it will be tighter and stay in position. My son has an Old Country Pecos, and his is the same as mine.
I add from both from the top and the side door, so either or will work. After I add the split, I open the side door open about half way or all the way depending on how high the heat gets. I've even been known to prop the top door open if I add too much wood and the side door isn't doing the trick (I haven't had to do this much lately once I figured out much wood to add). I'm doing a couple racks of spares on Saturday (almost 3 weeks w/o using it is killing me!) so I'll take a few pics and post to show my process. I did notice though that the smoker was running a little hotter w/ hickory and pecan vs. oak, so don't forget the time of day, weather and what kind of wood you're using will all have an affect on temps.
The nut on my intake dampener is a little loose, but not to the point where it restricts me from adjusting the vent properly. It's just loose enough to where it gets hot and the metal expands, it's still functional. On my brisket smoke, it expanded just enough to where it felt like the vent on my Webber Kettle.