Roush S1I Blower: Belt Slipping - Resolution/Fix?

Series II Blower: Belt Slipping - Resolution/Fix?

Has anyone had a problem with their belt slipping on ther blower pulley? I'm running a Chicane 66mm on the Eaton M90.

PROBLEM:
My boost will go up to about 10 PSI through the mid-range but fall-off near the top-end (approaching redline it settles to about 6 PSI). Could this be my belt slipping or might there another problem I'm not aware of. This wasn't a problem on the stock blower pulley.

I've pasted some of the raw, uncorrected dyno data below if that might help. Look at the data from 4800 RPM -->5400 RPM which seems to correlate with my problem. Also, the data stops at an A/F of 10.00, but the A/F actually goes to about 8:1 where you see 10:1 (that's what is making me think the blower is slipping):

RPM x1000 hp Air/Fuel
4.50 271.69 10.63
4.60 275.44 10.37
4.70 275.91 10.03
4.80 275.21 10.00
4.90 273.81 10.00
5.00 263.25 10.00
5.10 256.10 10.00
5.20 255.80 10.00
5.30 245.63 10.00
5.40 272.24 10.00
5.50 285.10 10.00
5.60 293.34 10.00
5.70 313.41 10.01
5.80 317.36 10.40
5.90 320.13 10.93
6.00 319.19 11.05

If it is slippage, is there an idler pulley or something that might help?

Thanks for the help/suggestions.

~ Billy
'01 S281-SC #201
'99 S281-NA Cobra #357