OK, I have the Atomic EFI on my 455 Stage 1 (all stock, with HEI). Over the last few times I have had it out it developed what felt like a misfire condition. So, I have all new: Cap, Rotor (MSD), Accel 8mm wires, plugs, radio suppression condenser. I ran all the wires to the HEI, under the cap and to the pick up. The module tested fine. I think we can eliminate that as the source. Next I had an O2 lead that shorted to the exhaust manifold. (that must be it?!?). Fixed and no change at all. The fuel system is set-up as "Returnless" single feed to the unit. My idle FP is 36-38lbs and idle speed is set to 720 rpm. The "squirt" is set to 19. The engine does fire right up and seems to idle OK. But as load is applied the car feels like it is breaking up in the ignition. At cruise speed 2400-2600 car seems fine. So any ideas from the group? I will be re-running the grounds at all points and adding a block ground to the frame. May need to seriously consider a return system using the Corvette regulator.