VMax 225 water presure on Tritoon

I am having a similar issue as (jjk61083 Thread 2002 Yamaha Vmax 250 OX66 Overheat Alarm ) I have a 28 foot Playcraft Tritoon and pretty much since the day we purchased it we have struggled with water pressure issues. In fact we seized the first 225 Yamaha not knowing what the problem was. Since 04 we have had a lot of the same issues with the new VZ225TLRC as soon as you exceed 3500 RPM pressure drops off completely. If you slow back down the pressure slowly comes back. All the techs including Yamaha and Playcraft say they don't know and they've had no one else complain about this issue. I finally installed a temp gauge to monitor engine temp

I've done all the same repairs including complete water pump kits and poppet valve replacements but nothing fixes the issue, there must be a substantial amount of cavitation that causes the pump to lose prime.

I'm to the point that I am going to install a low water pickup somewhere on the boat where I get clean water away from all the white water