Did you take out the lifters at all when you did the head gaskets? What did you touch at all that had to do with the cam and lifters? It sounds like either a lifter or cam lobe going away, either one being not good at all. Did you use new rocker arm nuts? If they are the stock type, they aren't made to use over and over, and it might be that the one in question is just not holding any more. (I doubt that is it) If this problem came on suddenly after you did the engine work, it almost has to be related to something that was done. No problems like this with this engine before along these lines? John