If it's the bowl size people would be running out of gas a lot. You'd think [or I would] the carb would have an inlet large enough to feed the bowl and maintain a proper level even when full throttle. I went over the Coca-cola highway at mostly 100+ mph. Some of the long hills are 7-8 miles long. In fourth gear the rpm was just over 5000, not 6-7000 as it would be at the track but high enough for long enough to drain the bowl if it were not getting filled fast enough.
The trend these days seems to be large pick-ups, 3/8 to 5/8 inside diameter fuel lines and pumps made to feed a high pressure injection system. All that gas we have moving still has to go through the 0.110" to 0.135" orifice in the inlet seat.
I'm no expert on Q-jets, but I have heard tell of a couple of items which could give you a lean feature at WOT.
First is fuel stacking in the bowl. Long hard acceleration or cornering can push the fuel against bowl wall, that fuel can lift the float and cause the needle to stop flow out of the seat. Do you have a Pontiac Q-jet or one made for another brand? They all have suttle differences. I think there are 20 or 30 different shaped floats for Q-jets and they can also be modified by cutting them.
The other is the secondary fuel metering, you've most likely changed the secondary rods and hanger a few times to get flow, but if secondary flow is still too low even with smaller diameter rods or a hanger that will hold the rod higher, the orifices can be drilled from 0.160" to 0.197". Of course it will be rather difficult to restore to the original diameter.

Your "stalling out" at the 1000 ft mark, are you sure it was fuel and not the point when your camshaft stopped increasing the horsepower? Mine flat lined at 535 all the way from just over 5500 to just about 6600 when it started to drop.