Isx Cummins turbo

Hey I have a 2010 prostar with the cm871 isx it's been deleted for a couple years now i just had it rebuilt a month ago. Before i rebuilt it the turbo was blowing a little oil in through the CAC so i had the turbo rebuilt along with the engine but 6,000 miles later it's blowing oil again i was told there is a restriction somewhere that's causing hi crankcase pressure or maybe the turbo oil return line has a restriction any ideas would be appreciated and also i was thinking of taking the vgt turbo off and going with a older style turbo but I was told they don't give as much power as the vgt i would like to know if someone has tried this and how was it with ( power, fuel mileage, engine brake) thanks