You just need to learn your pit sometimes there is a larger learning curve. It may help to remember that on an offset your cooking in a Zone. My Zone is 275-325 zone and I consider 300 to be my ideal cook temp. I start with a larger fire than I cook with this will establish a good bed of coals and preheat the pit min 1 hr I will let the pit get as hot as it can during this time and keep an active fire. once I finish the pre heat I add a split cut back the intake damper and set about doing my prep while the pit settles back to My Zone.
A few min before I set the meat load I add another split, load it up and close it up. When the temp drops to 275 I add a split it will run up to 325 and slowly fall back, repeat as necessary. IF for some reason(rare) I have a difficult time keeping the coal bed I will add some lump along with a split. Don't beat yourself up cook where the pit wants to run and adapt to it.
I never met a Cow that I didn't like with a little Salt & Pepper! Certified PORK-A-HOLIC