318 Retards Under Load?

Ok, this started after I filled up at a little country store in the middle of nowhere, back in mid January. A week later, I started ripping apart the motor, and everything looked just fine. Upgraded the ignition box, did some other stuff, started her up today, and it still falls flat.

Basically, under load, the motor retards, it feels like putting it in 4th from a dead stop, but if you let off and then punch it, it picks up, then falls off again. Has anyone come across anything like this before? I don't mind replacing bad parts, but it seems like a waste to try shotgunning parts, hoping for a fix. I thought about water in the fuel, dumped in some alcohol, no effect. Maybe the fuel pump is on its way out?

Thanks, Alex