I had that up hill/down hill problem with a 1971 Blazer. It was the carb float bowl/accelerator pump well starving for gas. Rochester has baffles. I got new Quadrajet and it stopped. I seem to remember that a product improvement was made on the Q-Jet. Maybe you are missing the baffle. (You probably don't have a Q-jet).

Could just be float level/float drop setting......or a vacuum leak.

Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn