Not always something you can "turn back into" a different burn quickly.....
1st look at possible cause......even slightly damp charcoal will cause a slower, dirtier burn.....not even like rained on.......just a bag left out where dew or moist air can get to it.......
Same basic thing with wood....if it's picked up some moisture, just enough, you'll get some slowing of the burn......
That's one aspect.......
Another piece of it is having the fire hot enough at any given time to not slow or stop the draft, or smooth airflow, thru the cooker......what you'd want to look for is the smoke "pushing" out the exhaust vent.....that's a visual check that tells you the airflow is fast & smooth.....
If the fire slows or 'dwells', you get chugging white or gray smoke, assuming the fuel is sufficiently dry like above.....
Possible fixes might be :
Make sure you have good & dry fuel of any type (I don't assume you're leaving it out & getting wet or damp, just a thing to watch out for)
Make sure you have a thick enough coal pack & are starting off hot enough to keep that burn going that hot or slightly higher
Attempt to start off reasonbly close to your constant running temp.......I like to start a little hotter, but not much, as the cold meat going in will cause a drop......if you start off way higher up, it
CAN run the risk of choking the fire if you're trying to bring the temp down too, too much........
Pre-heat the wood chunks on top of the cooker to get them somewhat closer to burn heat.....that will help them catch better & be less likely to chug & smoulder.....this , i guess, would be if you're adding in....any chunks already in would be heated by adjacent charcoal.......
Any kind of lower heat cooking is a little tricky, in that you're teetering at the burn point.....a little high, burns fine.....dip a little low, puffy dirty fire.....
Hope this helps......