I believe the opening from the firebox to the pit is too small, causing draft problems. There is a formula that needs to be used to get the firebox to pit opening size, the gap at the end of your smoke shelf and the diameter and length of the stack. Increasing the length of your stack will increase your draft.
My reverse flow has a 10 degree difference from one side to the other, but is also a LOT bigger.
PM me and I will see if I still have that spreadsheet with the calculations on it.
Nice looking build, though!
JayBirde,Team Captain of Limp Brizkit BBQ www.LimpBrizkitBBQ.com (Work In Progress)