Yea, I saw your other post after I suggested that.
I would check to make sure all your baffles are open and make sure that there isn't anything blocking the tubes from the Fire Box into the Smoke Box.
Then, when you start the fire initally, have all the baffles open as well as the door to the Fire Box.
Once the fire gets going, then close the fire box door and close the baffles on the top about 1/4 so that they are open 3/4ths.
I would be surprised if you could not get it up to temp doing this, there would have to be another reason as this should easily bring it up to temp.
Sometimes when I put too much wood or charcoal in it initally, I get the temp too high, 350 - 400 and I have to let it burn down before I can throw any meat on it.
Let me know what your results are on your next cook.
Good Luck!!