sudden drop in rpm's

When it drops in rpms it is smooth like I just pulled back on the throttle.  But then after several times doing that it got a bit rough.  I saw NO drop in fuel pressure during this event so thought it could not be some issue with fuel...could it still maintain fuel pressure and have a drop in rpms due to fuel?  I do have a fuel pump and when I turn it on it jumps up about a pound which has been normal since new.  

Your fuel flow issue may be after the fuel pump. The hose off the bottom of the mechanical pump that feeds the carbs that went through banjo bolts my have some debris. Blow that hose out up to the carbs. Remove the hose off the carb so the fuel and or debris will blow out. Check each banjo bolt for debris. These are located at the cross over balance tube between the carbs on the assembly mounted there and then at the carbs themselves. Some aircraft don't have the fuel block assembly and only have barbed tee fittings. leave no stone un-turned.

Have you checked the carb bowls for debris?

If you have a reduction in flow after the pump the pressure would remain the same.

Retracted.

Not disagreeing with anything you wrote and probably not the original poster’s problem since he has new carbs but I , a few years back, did experience engine rpm drop due to carb debris and , surprisingly to me, it was not rough at all - just a smooth rollback to about 4000 or so as if somebody pulled back on the throttle.

And I do have a video to prove that it actually happen :-)

https://youtu.be/PCmdNnOrXOc

UPDATE:  Still have not found the problem.  I changed out the fuel filters and blew out the fuel lines.  I also changed out the oil and spark plugs.  I am desperate!  I have a friend that will help me look down the cylinders to check for anything.  I did do a compression check.  78/80, 78/80, 76/80 and 71/80.  Would that one cylinder cause this issue?  Does anyone know of anyone that would be willing to come help me (I would pay them of course)?  I live in Cleveland, GA.