Datalogging a Rzr on the street question

I've been tuning a Rzr with a custom installed turbo system. I've been trying to get the VE scale dialed in by doing dozens of runs while datalogging. I thought I had it pretty dialed in until today I noticed when I applied the footbrake(brake switch is disconnected) to create extra load that the AFR when way lean compared to another log doing a full throttle pull with no footbrake. So, my question is what do I need to adjust to maintain the correct AFR whether under heavy load or light load? Tia