Fuel Pressure Issue

We have a 2011 Mobius LSV with Indmar 325 Assault. Fuel pump and filter are inside fuel tank. We hooked up a fuel pressure gauge and when idling it is perfect at 60 psi but once we put it in gear and throttle up the pressure drops severely, the more throttle we give the lower the pressure goes. Also when we shut the boat off the pressure drops to zero. This is why it idles fine but will not get over 3000 rpm's and backfires when you give it too much throttle.

I'm guessing the pressure should stay even when the boat is off? Also, what could be causing the pressure to drop when throttling up? Bad fuel pump? Bad fuel regulator or something else altogether? This fuel pump is $664 from Moomba so I'm trying to confirm it is the pump before dumping a ton of cash into a guess.

Anyone have any thoughts on this?

fuel filter issue?

Fuel filter is in the tank and attached to the pump. It seems like a fuel filter problem but I dont think that would cause the pressure to drop when the boat is turned off ?

Your fuel pump isn't keeping the pressure up , when it's running the boat is using the fuel and pump can't supply enough.
When the engine is not running and you put the key in the on position the pump should start and prime the system and shut off in a few seconds 3 to 5 . If you have ever run out of fuel or run the boat with very little fuel in it the pump can burn out .

I removed the pump last night and it was cracked in half. There is a white plastic shell around the pumps, filters, etc. This plastic is completely cracked in half, no wonder the boat hasnt been running right for so long. I talked to Moomba and they say the tanks come to them with the pumps already installed. I have no idea how this pump could have broke just sitting inside the tank?? We ordered a new pump, $664. UPS lost the first one so SC is sending another pump today for saturday delivery. This has really been a mess but hopefully the new pump fixes this mystery issue once and for all.