Misfire with lower than 1/2 tank of gas

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I’ve been chasing what I have thought is an ignition misfire and the more I’ve been driving my truck as a daily driver it seems that the issue starts to happen when the tank is below 1/2 tank. It seems to get worse the lower I get on fuel.

For reference the truck is all stock original 1970 C10, fuel tank in cab, big block (not that should matter), 62k miles, been garage kept most of its life and never left non-running for more than a month or two (like it didn’t sit for 20 years with same gas in the tank like my dad’s Pontiac did when I inherited both this truck and Pontiac when he died. My dad actually drove the truck and kept it running with fresh gas in it)

Question is gas anyone experienced this and was it a fuel pump issue or or sending unit in the tank? Could the sending unit have hole in pick up tube causing this? Or is fuel pump just too weak to pull the fuel from a tank that is low on gas?