Ummmm wouldn't turning boost down increase the richness problem ?? Turning the boost up would create more flow, more air, leaning out your richness.
But I wouldn't advise you to just turn your boost up - You really need a tuner with Dyno & Wideband Lamda probe thingy to tune it safely.
How do you know it is running rich ??
Do you have a factory ECU ?
What sort of car you got ?? I thought factory boost on a GTS-t is 7 PSI , so I don't think you will get it below that....