Blitz DUAL is a fantastic boost controller, seems like your tuner has no idea how to set it up, hece it's dropping. If you hold the left button down for 3 seconds, there's a GAIN menu.. increase that till your boost holds flat, you will need to drop your duty cycle down.
Also on the back of the controller there's a setting to put it on EWG OR IWG.. I hope you've set that correctly too.
AFRs mean nothing compared to ignition timing as I've mentined before.. you can have a lazy arse flat as shit low timing map with perfect ruler style AFRs..
Like I said, post up your microtech's timing map, or even the tune file.. I can put all those numbers into a three dimensional table for you and we can analyse it.. (sometihng micro ice age cannot do)