I have my ball valve up high like you do (fat and lazy mod) and do not have issues with the fire dying. As someone suggested above maybe you do not have enough of the top vent open. I usually start capping my intakes on the way up and the temp usually settles around 250 with the ball valve half or 3/4 open. The advice to wait a little before making more adjustments is invaluable.
[FONT=Arial Narrow][B]EZ wood handled 3 wheeler | OTS | OTS mod to OTG | [COLOR=red]Ladybug[/COLOR] SS Performer | UglyDrumTandoor | UDS v1 | midi UDS with [COLOR=red]red[/COLOR] [COLOR=black]nipples[/COLOR] | SJG smoker mod | Simpsons SJS | [COLOR=black]Simpsons[/COLOR] OTG | WGA charcoal | SJP | Stacked brick WFO | Lodge Logic Sportsman's Grill cast iron hibachi/sigri | [COLOR=green]LBGE | sbge | [SIZE="1"]mini bge[/SIZE] [/COLOR] [/B][/FONT]