Low fuel pressure, new almost everything ! Help

Yeah those little guys are very efficient, but they have no capacity, well they do but not for big stuff.Big stuff just piles up in front of it and then it's game over.You gotta run a prefilter somewhere. I went down to Napa and got a bigboy EFI filter with a 3/8 hose barb on one end and a fuel line fitting on the other. That beast is about 4 to 4.5 long and about 2.5 in diameter.I put it on the suction side, Which they say is a bad idea, but mine has been there since 99, and 125,000plus miles, so IDK. From the pump is a 1-piece steel line, with a short jumper at the dual-feed and I have no fuel-pressure gauge at all;never have had. I mounted that bigboy in front of the passenger side front spring mount, and ran a new steel 3/8 line up to the front stub frame, then into it and up to where the hi-output mechanical pump resides. I tucked everything up high and secured it as necessary.
If you don't have a pre-filter, follow RRRs advice; Remove the line from the pump, and the short jumper at the back and blow out the line. Then install your prefilter, blow out the line to the dualfeed,and finally those little GMers. Then see how it goes.I think you mighta just had some crud move through the system and it piled up at the carb. But if you don't blow out the lines, chances are that crud is still moving along, and it will strand you somewhere that you may not want to be stranded at.You can skip the line flush if you're willing to take that chance, but carry a spare filter.
I skipped the flush this one time and plowed through 4 filters in about a month. You know, those $2.99 ers. HYup, there was me on the side of the road again replacing a filter on the old Volare. Eventually that tank popped a leak on top,of all places. It was perforated in several spots where that sound deadener had trapped moisture, so I replaced it;and no more problems.
After the line is cleared you may want to check the pump's free-flow output.This is done by Tee'ing into the pressure side fuel line and running it into a container, about 2 quarts/liters. Then you start the car,let it idle for about 30 seconds, and shut it off. Then measure the quantity of fuel pumped, and convert it to liters per hour. But skipping the math, if it pumps a pint in 30 seconds at idle shes ready to hit the road.
The factory spec is 1 qt(32oz) per minute, or less, at 500rpm.
If you're going racing, you'll need about a half pound of fuel,per horsepower,per hour.This works out to about 68ounces in 1 minute for 400hp, according to my math.Yeah, so, that's a lot,eh;You might have to rev it up a bit to make that number,no biggie.
I skip the Tee'ing and just dump the line straight into the container; the engine will easily idle for the duration of the test, on the fuel that is in the bowl..