09 SAAB 9-7x Scaling LS7 maf issue

[99SLOWC5]

I have a customers 09 Saab 9-7x here. Truck as a fully built 408 with a D1SC on it. AWD still. Customer put a LS7 Maf in a 3.00" tube. by 5,100rpms the MAF stops growing past 11,500Hz. I thought I did everything properly to rescale it 20% but I believe I've missed something. I know the 3.00" tube is limiting me alot. Can someone tell me what I did wrong.


Thanks

J