Engine Struggling at high speed

Howdy Y'all,

My little 318 is REALLY struggling on the highway. I get up to about 75 mph, and she doesn't wanna go any further than that no matter how hard I push the gas. There doesn't seem to be a difference between half and full throttle. The car is a 78 Aspen with a 4spd manual tranny, 2 Barrel Carter BBD. Mostly stock, but with Pertronix Ignitor III ignition system.

I rebuilt the carburetor myself (my first time) and I'm wondering if I f*cked up the adjustment on the accelerator pump. Thoughts?
Author: RockStar1776