You did see the vents on the side, right? Apologies if that is a stupid question...
I've cooked on my Jumbo Joe a couple times now, most recently yesterday, and the side vents were sufficient. I only used half a mini chimney of lump and cooked 4 ears of corn followed by half a dozen brats and it worked fine. In fact, I had to close the side vents down to about half when I put the brats on since I didn't want too much heat.
I can also confirm that Cowboy Lump is now made from pieces of wood branches rather than lumber scraps.