I put some air back through the hose from the filter housing and air is pushing out the breather next to the filler port

The hose could be collapsing internally when it under suction from the fuel pump. If the fuel line hoses have never been replaced, they need to be strictly from a safety point anyway.

Like was said, it would be a good idea to run a remote tank. If the pressure does the same thing, then its the cool fuel pump. The pump by itself is NLA from Merc, but there are lots of aftermarket ones available for $100ish. Merc only sells the complete Cool Fuel for like $900

i just replaced the rubber line from the tank fitting to the filter housing. There is less than 3’ of rubber 5/8” line total. Hose maybe has 15 hours on it.

Update.

Replaced the fuel pump, and new regulator since I had all of that out 2 weeks ago, finally was able to run the boat, and back to running great. 5100 rpm, fuel pressure was steady 47-48psi and ran great!

Good to hear! Can you share the pump model number and where you got it, please? I'd like to have a spare pump but don't want to pay Mercruiser the big bucks for the whole Cool Fuel module.
Thanks!

I ordered this pump and regulator. I had to cut the top off the new regulator to put my Hardin adjustable set up on. I also bought a tube of super lube silicone heat sink to put on the pump side that contacts the metal plate. Fuel pump kit came with o rings and screen for the fuel cooler as well.

https://www.highflowfuel.com/qfs-oem...RoCbhcQAvD_BwE