Let's see your basket. It could be air flow or high sugar but with the little amount of information it's hard to discern. You said in your original post you tried different rubs, were any low sugar? Pic's of your product and setup would help us all.
FEC120, XL BGE, DigiQ DX2, UDS, Cimarron, Weber Jumbo Joe, Grill Grates, ThermoWorks RT600C