Pump vintage: Off of a 1997 502 MPI - V belt drive. Stock lines, fittings, all in good shape, stock power steering cooler used with stock mounting bracketry (mounted on port side cylinder head).
Add-On: Single Mayfair Add-on steering ram, 9" stroke plumbed with Brazil valve

Issue: Pump keeps throwing belt above 5000 rpm regardless of how tight or which brand/style v-belt installed. Pulley has been aligned to crank pulley with straight edge. No leaks in system. Generally going in straight line when belt is thrown. Engine has cross over cooling system so no water pump pulley involved. Belt goes from crank straight to pump. I did notice the pump spit a bit of fluid out of the cap but reservoir still properly filled.

Question: Is my pump bad? Am I somehow creating a dead head pressure enough to stall the pump and kick the belt? Do I not have enough reservoir capacity and/or over aerating the fluid? Engine needs to spin to 6000+ rpm.

Ron, look at belt width, make sure belt sits down in pulley correcly, the 6k speed might be a issue, ck with smitty on his setup as I know he turns his hard...

Bracket flexing under load?

I can't imagine so. It is a beefy bracket and everything is tight and braced as it should.

I am running generic power steering fluid in it. Is this maybe my issue?

http://www.summitracing.com/parts/amd-w-395

The fluid should not be an issue. Something has to be out of balance slightly and pushing it past 5000rpms is causing too much bounce in the belt.
I used to have the same thing happen to WP belt on a SBC drag car engine. It was fine until I pushed it over 6000 rpms. Beyond that and the belt would come off.
Replaced WP pulley with new and it was fine.