Loss of power in Chrysler 318?

[Alex]

Motor is a late 70's 318 block, 360 heads, Edelbrock ld4b intake, Edelbrock 1406 carb, new Mopar Chrome ignition box, 6 month old MSD Blaster 2 coil, new spark plugs, new fuel filter, new rubber fuel lines.

Problem cropped up in early January, right after filling up with ethanol free 93 at a little place in the middle of nowhere. Where it used to get up, burn rubber, then go, all you can get now is a sluggish slouch, and lucky to hit 35 mph. It feels a lot like throwing a manual transmission in high gear, and trying to drive it(but it isn't a transmission problem. Tranny shifts just fine). The motor has now been freshly rebuilt, drove it for the first time this morning, and the issue is still there. I've tried alchohol and seafoam in the tank. My question here is, could it still be bad gas that I could just drain the tank and refill on known good fuel, or should I check my float levels, or consider a new fuel pump?

Motor is in a 73 Plymouth Duster, as if that makes any difference.
Thing is, when the problem cropped up, the build was a few years old. It popped up early January, and a week later everything was torn down for the current build. We re-used the fuel pump, which is why I'm finding it suspect.

There's no smog bits on this motor, and with the Mopar Purple 360 bumpstick, it puts this full interior Duster over the line in the low 14's, with highway 2.73's

[DonR]

A fresh engine is stiff as aw getout. Let it break in before putting it through its paces. Give the rings a chance to "bed in". How are the valves? That engine needed leaded fuel to prevent the valves from receeding into the seats, but that would take several months. Maybe you had the valves and valve seats updated when the engine was rebuilt. If you put the old heads back on without giving the valves any attention, check the lash. Make sure the float does float. Put it in a bottle of gasoline to see. A heavy float can leave you flooding all the time. Good luck.

In the late 60's the 318 was a ferocious beast, but by '73 smog equipment stole almost half its power. I hope you're getting more than 150HP out of it. The '73 360 only made 175 HP.