Engine Starves for Fuel When I Hit Second Gear

[Old Yeller 1970]

After a forever restoration/rebuild project I'm finally getting Old Yeller out of the garage and back on the asphalt. No surprise I still have some bugs to work out and this one has puzzled me for a while. I'm running the engine described in the signature. The truck comes out of the hole hard but when I shift to second you can tell it isn't getting all the fuel it wants. It really falls flat and you can tell it's starving for gas

I have the fuel bowls set a little low right now and I'll raise them tomorrow but it was doing this when they were high. I have a Holley mechanical fuel pump that is rated for the HP of my engine combo. However, Barry Grant says a 625 Road Demon should have at least 6-7 1/2 PSI of pressure on it. Today I noticed (at idle) it was sitting around 2 1/2 - 3 PSI. This is the second Holley fuel pump I've had on the engine and I hate to toss out another one if that's not the problem. I wondered if the stock fuel lines could be at fault? Could they be restricting the flow? It seems like that wouldn't keep the fuel pump from delivering enough pressure at idle. I could also have an issue with the pump rod not actuating the pump correctly I suppose? Maybe I should ditch it and put on an electric fuel pump?

Two other items of note, the fuel tank is a new Blazer tank and new sending unit mounted under the bed. And BG says that with my cam I should be running a 650 Mechanical Secondary Speed Demon. If money were no object I'd buy one and bolt it on. But money is an object and I have to make do with what I have.

Here's a photo of the finished product.