Underdrive Power Steering Pump Pulley Question On Supercharged 4.6

I have a 1999 mustang with a 4.6. I use it for track days at road courses. Over the years it has evolved to a forged motor, pistons and rods with stock crank. I have a procharger supercharger and I'm making 585 rwhp. The belts were slipping previously at around 5000 rpm on the dyno so I went to a 8 rib set up. My tuner recommended going with a overdrive crank pulley and underdrive water pump pulley. It corrected the slippage problem and we increased from 550 to the 585 rwhp. The last time I took it to the track the power steering pump seemed to go out. I had on and off power steering which is not good at 140 mph on the back straight. But once I got it home and drove it on the street the power steering worked fine. I am going to replace the power steering pump anyway since it is the only stock part left. I intend to add a power steering cooler at the same time. My concern is that the overdrive crank pulley and the higher rpm's I'm running may be causing cavitation. Has anyone else run into this problem? Where can I get an underdrive power steering pulley? I only have about 1/2" from the power steering pulley to the crank pulley. Any advice?
Thanks,
Ben

My tuner is good at what he does, but he typically works on drag cars and they don't run sustained rpms like I do