Cam gone flat? Here's a interesting video.

Yeah do all the right things like proper break in oil, cam lube, get it started right away (make sure everything is right with fuel, cooling and ignition and you have a timing gun ready to go), hold above 2000 rpm for 20 minutes and that is all you can do. Of course light springs for break in will help if you have heavy springs in it.
And check the lifter bottoms for convex and measure the cam lobes for taper.