Sounds like a restriction somewhere to me. I just zoomed in to have a look at your filter head. Looks like you put the gauge in the schrader valve location. If memory serves, I don't think that will tell you what you need to know and it's probably why you don't see a pressure drop. I tee'd mine in on the back port where the stock pressure switch is. I'd move the gauge and watch it. I think it's lying to you where it is.
Here is my setup.
Fuel pressure gauge to the back, return line in the middle and schrader valve in the front.
Here is my setup.
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Fuel pressure gauge to the back, return line in the middle and schrader valve in the front.