Losing fuel pressure on new setup

Well i swapped carbs to a 600? Cfm holley i had laying around. Dont know much about it other than its old and worked the last time i used it. The car ran without a hitch with the other carb so im going to throw a kit in my good carb and reset the float levels. The weird thing is my pressure still did the same thing. Went from 7 to 2. It seemed to take longer but it still dropped.

Any chance its a faulty gauge? The car ran and drove for 30 min without a problem

My next plan is to put the good pump and reg back on with this carb and see what the pressure does and how it runs. I will also add clamps on my rubber connections as suggested to be safe and see If it changes anything