help with fuel delivery issue, please!

[OJ1988]

Okay, this is on my daily driver and is becoming an issue.

First vehicle info.

1969 Chevy C10 truck, original except where mentioned.
120,000 miles.
250 6cyl
3 on the tree

About 2 years ago, installed a
clifford intake,
450 holley mechanical secondary 4 barrel carb
split headers with glasspacks

about 6 months ago added new HEI dist.

carb was rebuild about 6 months ago as well.


Here is the problem.

When driving at sustained speeds over 50 mph, after a distance of 5 miles or more, it will fall on its face. Basically like you shut off fuel to the motor. Pulling over, stopping, and taking back off does not cure it. It will run at low speeds, under 35mph fine, but if you get on the gas it does nothing.

Now, I can drive around town for hours and it never does it.

Typically on the highway, I could make it about 10 miles, which is great, because I drive 8 miles in interestate to and from work. Sometims it will do this at mile 4 though which can be a problem.

It does not seem to be affected by temperature, or any other factors. Sometimes it does it sometimes it does not, but there never seems to be any corralation the times it does it.

When it first happened I changed the fuel pump, fuel filter, and sprayed cleaner in carb.

Any ideas?