Catching temps on the way up is key.
Making sure you only light a few briquettes is also important...I've done 12-15 before (usually do 7-10) to try to speed up the process of getting the drum to temp and all it did was make it difficult to manage temps the whole cook. Now if you want to get 300-350 it's not bad to do a few extra, but even that can be achieved with only a few coals to start. Doesn't seem to make much sense that 5 or 6 more coals would change much but in my experience it does.
Also checking for leaks could solve some problems. I didn't squeeze my lid down tight one time (it was on...just not pressed down and sealed all the way) and the temps started rising real quick. Thankfully I have my digital thermometer and caught it before it got too bad...doesn't take much to mess things up.
Golden Dome UDS | iGrill | Blue Thermapen. Where there is love there is barbecue. – Gandhi