Either the AN490 or the spherical rod end MAY be the problem. There are thread gauges which show if the right number of threads/inch are present and also thread micrometers with conical tips that can measure the root diameter of male threads. These may help. If you don't have them a friendly machine shop may help.
A cheaper alternative is to get the same thread size AN bolt and nut. Thread them together to check them, then thread the nut onto the AN490 and the bolt into the spherical rod end. This should indicate where the problem is.
I would not recommend using a die on a male thread, as already stated the threads are rolled. If the AN490 threads are the problem I would buy new ones.