View attachment 3871
The blue arrow is the unloader's bypass. When pressure is running lower than it's supposed to and the unloader is working properly, there should be no flow out of that port. The gauge is reading pressure direct from the unloader's outlet (obv. red arrow). This means some of your flow is going somewhere, could be the unloader, could be a valve somewhere opening when it shouldn't or leaking by, could be the pump not getting enough water or drawing air (a very likely place would be that tubing fitting right below the red arrow, those fittings are crap). If it's not a massive amount of work, I'd try to get to the unloader's bypass and try to route it into the tank where you can see flow or into a bucket so you can tell if there's flow when the pressure is low. This is just a no-cost way to confirm or eliminate the unloader as the problem.