Fuel spark delivery question

[Robert8096]

I have a 69 truck with a 283 and have a nagging problem where the truck runs fine up till about 50 mph. After that it will start bucking and acts like it is not getting spark or too much or not enough fuel. I can back off and it will continue for a few min and then go back to running normal. Did a compression check and all are 150 to 153 PSI. Vacuum gauge reads a steady 19hg and responds correctly when working the throttle. It was an original point type ignition and I have changed it to HEI, replaced the wires and plugs. I replaced the 4 barrel carb with a known good one and my problem still exists.

Things that have got me saying WTF:

I looked for a fuel filter between the fuel pump and tank and there does not seem to be one. Is this the norm for the old girl? I have one between the pump and carb and I am seeing a little bit of rust in that one but nothing major. Is there a sock on the end of the pickup tube in the tank? I ask this because LMC shows no sock but CPA shows a sock on their sending unit. I also see that there is a difference between the 6 and 8 pickup units for the tank. Is this because of fuel line size and if so will that make a difference in running a stock 283 in a truck that was an originally a six?


When I changed the plugs I came across what is in the pictures below and see no reason for it. There was nothing wrong with the threads of the plug hole as I replaced the plug and had no issues. The extra piece looks to be a compression tester attachment. Any ideas on this PO install?

Thanks
Robert