No boxes. And boat had good water pressure when we first got it in Nov '12. It has changed over time - and end of last year (our first season with it), it had same pressure it does now.

I just called local parts house - they have one set of balls and springs left. I'm picking them up this afternoon. I'm hoping that helps, but my understanding is loose condition causes idle overheat - not high rpm overheat. (??)

I hope you're not just messing with me! ...loose balls, tight balls, hangin loose - did make me laugh. But when I checked mine, my balls were loose too!

It sounds like you have a hose collapsing based on this.

I don't joke about my balls!
The whole thing has been frustrating for me.
With Bravos I had 23psi
With SCX-4's and through hull PU's I had 4PSI unless I buried the PU's all the way which isn't right
So I made a 2" notch feeding the PU's-nope
I made an 18" notch feeding the PU's-nope
I changed the strainer configuration-nope
I ditched the Hardin SS pumps and reinstalled the plastic ones-gained 4PSI
I installed a different contour PU-gained 4PSI
I installed new balls-nope
I installed new springs-gained 10+psi
There is one other change I made. After I changed the contour of the PU and gained enough pressure, 12psi, to run WOT without overheating....FINALLY!!!, I filled the engine with water. 575SCi intake rot. So I welded and machined the manifolds and installed the new springs at that time. Of course, after I repaired the manifolds I get a spam from KE with their NEW 575SCi intakes for $750 each. I saved $250 per manifold but they're not new and hardcoat anodized.
I asked about the balls a long time ago and nobody said anything about them. I figured it was a PU problem because I had changed all of that and it was fine before.
If yours was fine before it has to be a restriction or worn out part.

What else have I learned about 575's besides intakes and balls?
The head gaskets blew so I did them, you've read about this I'm sure.
Then a cam broke, I've read that this is a problem too. Went .030 and hydraulic roller.
Fortunately I have the better blowers, oil bath front and rear. I change the oil every 25 hours, and bearings and seals every 100 hours or so. The bearings have never been bad and I have the 3.5" pulleys.
I've never done anything with the computers. Mine runs pretty clean unless I get to elevation where it'll start rich but clear out fine. The dyno pulls showed good A/F as is so I left them.
Last thing I learned is that bravo props last 1/4 boating season and Max's last 2 seasons. XR's last 100 hours not 104.

We've had a bunch of rain here - so can't test any of the minor changes I've made. I did pick up the nylon balls and springs last night, and I should have the sea pump suction hose on Friday. Hopefully, I'll be able to dunk it on the trailer this weekend. Unfortunately, the Ohio River is rising 12 feet in the next 24 hours, so no boating locally.

Do you have a go pro you can put in the engine bay and run with it on?

Yes. What do you suggest that I look at with the camera?

Looks like some of the guys would like a shot of your balls while running hard in the buff.

http://www.youtube.com/watch?v=-XmdQGsUX8A

Make sure the lights are on.

Unfortunately, I don't have strainers.