Possible those issues come from running a thermostat w/ the bypass hole plugged? If the thermostat is closed then the pump is deadheading and may cause some issues?

Meziere says not to run a thermostat w/ their electric water pumps, so I don't. I use the pump that fits in the stock housing obviously.

I have the bypass plugged w/ an 1/8" bleed hole on the 440 that's in my dad's road runner street driver. No issues w/ that one, runs nice and cool even in the summer heat here. It is a pretty mild build though and uses a belt driven clutch fan and water pump.