If its on the warm AFR should fluxate around 14.7 regardless. Did you mess with the warmup enrichment? (I dont have Nistune so im not sure what exactly you can mess with) Do the coolant temp (as read by the ECU) seem sound? If the ecu thinks the engine is warm when it is not this will happend. Is the injector latency set correctly? Personaly i think i would swap the DW`s and get that out of the equation right away. They are not doing anything good for you in this matter anyways.