As we all know their is 4 or 5 manufactures of AR 15 lowers that manufcturer for all the major AR 15 Rifles Aero design being one. Who are the main manufactures of the AR 15 upper receivers?

Do you mean foundries?

4-5 was accurate several years ago.  It isn't anymore.

4 or 5 companies make FORGINGS.  CMT, LMT, and a couple of others make a lot of stripped upper receivers but there are shops all over that finish machine them.  Some vendors do it themselves and some purchase the finished product to build into rifles.  So it really depends on where you got it and who they bulk purchased from (and vendors can change suppliers pretty often).  For most uppers you may never know who did the finish machining on it because the only markings I have ever seen were forge markings unless it was a company logo.