take a good close look to see if it there's debris embedded in the bearings. did any of the bearings have to be reamed or scraped to make the cam turn freely? that raises another question, if the cam didn't turn easily with 2 fingers during the assembly process, it was too tight.
can you take a picture of the cam bearings and the main bearings to post here? obviously, main bearings installed wrong could keep oil from the cam bearings too.