The original configuration of the Pantera fuel tank has a fuel tube pickup that is welded to the interior of the tank and is separate from the fuel gauge sender.
It is steel. It has the tendency of rusting through at certain points along the tube. Most common is around 1/2 tank level but there is no guaranty where that hole in the tube could develop or when. That would effect the fuel pumps ability to siphon fuel through the tube because the hole would break the vacuum.
The only way to test for certain would be to set a separate pump, independent of the engine, and see if you get flow through it.
Mine rusted through at 1/2 tank. The car would run no problem with a fuel level above 1/2 tank. Then die at that level.
There is a replacement for the pickup tube that is part of the fuel level float sender. I installed that and it corrected the issue.
The other thing to check is that the tank vent is open and not clogged or closed. The original filter element used in the factory vent is a little funky and can clog due to age. That one I believe is riveted on. You would need to drill out the rivets to remove it.
If it is the original supplied on the US delivered cars you might want to put in the later type that has roll over check valve built into it?
On my car the factory charcoal fume filter is long gone so I vent to the atmosphere. It originally was connected to the tank vent and then breaths into the factory air cleaner. I've never heard of one clogging but it is part of the tank venting system and they were serviced new. The car is 50 years old now. So who knows it's lifespan?
Any one of these scenarios could cause no fuel to get to the engine.