Is it new or used? Every time I've had any issue with any of my eggs not reaching temp a good cleaning always fixes it. Pull all of the guts out and clean it good. I use the small shop vac ($19 at Wal-Mart) and it makes quick work of it. Make sure to clean the round holes in the firebox and make sure the vent screen is clean.
The ceramic cap allows you to put the cast iron cap out of the elements to prevent it from rusting. Run a strip of gasket material around the lid at the top and the ceramic top will seal better saving more of your lump for the next cook
