It looks like you have the exhaust damper almost closed in your cook picture. I run my Cimmaron with the exhaust wide open and the intake damper open just a sliver or closed and maintain 250-275 all day. The only mod I have done is to put in an expanded metal shelf in the firebox to keep the coals about 3 inches off the bottom; the one that comes with it will get choked out with ash real quick.
Weber 22.5 One Touch Gold w/ Rotisserie.
Brinkmann Cimmaron with turkey fryer and log lighter.
Stovetop, Camerons Gourmet Mini Smoker.
Future UDS Owner (slow build mod)
Smokin' Fast, Splashproof, Blue Thermapen
Airborne! God Bless our Troops!
Member of the Zero's Club
CLICK HERE to visit the BBQ Brethren Throwdowns