I would try to disconnect the exhaust system or just drop it at the manifold. Thats after a few checks below. The power after it warms a little is probably just the oil thinning out a little with heat.
Since it starts so easily I wonder if your description is right on compression? Some numbers might help. You are getting the injection pump opened up? Or is there too much slop in the linkage? See if the linkage fully advances the pump arm with the pedal. You would not be the first.