Is It The Fuel Pump?

So what is your idle vacuum,and idle timing? and
is the Vcan working and plumbed to the spark-port? and
what are your cam-specs,and either; true compression ratio or cranking compression-psi?
and TC stall? and rear gear?

Because it starts right up, I think your pump itself is fine.
Because it usually stalls with throttle tip-in, this is lean-running; usually an accelerator pump issue.
Because it has also happened on other occasions, and associated with inclines, and no tip-in? , fuel-level in the bowl, is a good place to start.

But
because it always starts right up, AND is seems to always be associated with transitioning from idle/near idle, IMO, the fuel level is pretty close to perfect, and the A-pump itself, is probably OK.
Since you didn't mention an idling issue, or a change in idle quality; Ima thinking the low-speed circuit,the T-port sync,the fuel itself, and liquid fuel level are all OK.
That just leaves the pump-shot timing,it's quality, and it's linkage adjustment,and/or the idle speed, and/or......... the power valve system.
Of those, I would check the linkage first and then the PV system.
The pump must deliver fuel the instant the throttle-valve is tickled,however slowly.And the fuel must be "streaming" liquid fuel, not dribbling,or full of air bubbles.
The powervalve system, metering rods in your case, must be activated at about 10 inches of manifold vacuum. This can be varied downwards for a bigger cam that idles at less vacuum; but I find 11 to perhaps as low as 8 to be very driveable.

So I would check/adjust the linkage first, and then I would install a manifold vacuum gauge with a long enough hose to be viewed from inside the car, and then go for a ride. I would try to associate the issue with a particular manifold vacuum, and a particular throttle position, and a particular road-speed.If you can do that, perhaps you will discover that the PV system is tardy.More powerful springs will be the next change, and a new roadtest.But the pistons must stay down at idle! And if they come in too quick, fuel consumption will suffer. They must also stay down at 65mph under steady-state cruise; so check your vacuum at 65 mph. This is usually not a problem.

The Vcan may not become active until 15/20 mph or so. Because of this we often run a tad more idle-timing, and get the mechanical advance mechanism started as soon as possible perhaps as soon as 200 or 300 rpm above the idle speed.This will increase the engines very-low-rpm torque, and help cover this sometimes hard-to-solve issue.
I good results with the the following
idle timing from 8 to 16 degrees,(the smaller the cam the less the timing). But I try to get the advance system going by 1000 rpm and for it to be around 28* by 2800, 36 by 3600 or sooner.The higher the compression ratio, the faster it usually takes it. But some combos will detonate under load if it comes in to heavy or too fast.
If your idle-timing is too high,it will upset the T-port sync.If it comes in too fast, you may get detonation, especially in conjunction with V-can timing.
If the idle-timing is too low,or too slow; torque suffers and you may experience driveability issues.

So what is your idle vacuum,and idle timing? and
is the Vcan working and plumbed to the spark-port?,and
what are your cam-specs, compression ratio or cranking compression-psi? and TC stall? and rear gear?