I resisted the urge to burn my piece of **** to the ground again today, it just doesn't run right, will wind right up without a problem in neutral, full throttle blips open the secondaries fine, but take it on the road and it's a complete slug. It has 4.10 gears in the rear end but it won't even break the tires under any circumstance. Getting really frustrating, I took out the MSD distributor that came with the car, put in a known good stocker, same story. I have good fuel pressure, (mechanical pump, 6 psi), fuel line is clear, new tank and sending unit, new 650 AVS2 carb. 360/727 with a mild cam and TTi headers, had the near exact combo in a Dart years ago except that one had crappy smogger heads and it was a screamer, even with a stock cast iron intake and thermoquad.
Did you check your plugs, compression and how old are the plug wires? Pull the intake and check the lobes? Check the pushrods, are they bent? Valve springs, stuck open valve(s)? Did someone do an LS swap when you weren't looking? Had to ask...
edit:
just thought of this, did the timing chain slip a tooth?