1997 f250 5.4 triton changed harmonic balancer and now it falls on its face and almost shuts off until I cycle the key while still driving, then it runs great for about a block and does the same thing. I've changed all the plugs with motorcraft plugs, and cool packs, I'm lost at the moment so any info would help greatly, first module ford engine, have delt with multiple 5.0's

 

I suspect what may be happening is, the system is detecting a fault and is going into"Limp mode" with reduced power to protect the system and vehicle.
That could be why you are able to reset it by turning the key off then on.
Suggest you carefully recheck all your work since you didn't have this problem before the work was done, OR did you?

One thing that comes up is , why did you change the crank pulley and where did you get it? They are NOT all the same.
Are you able to have it checked for any codes in the PCM?