gear oils need changing,need info on correct oil/type

[73GMC10]

Hi all, that's all this forum needs is another oil question, I have researched for about over an hour and I think im going to go with 80w90 for my dana44,sm465/np205,14bolt ff rear end, now as everyone has diff types of oil recommendations I just want to be clear that from the d44 front,tranny/tcase/rear end 80w90 is fine.
But what is not answered though is positive and negative talk about GL-5 oil, people are saying use it, its recommended and others are saying no don't it'l eat /do harm to your parts inside especially the tranny and tcase, so just want to know if anyone can help me on this gl-5 thing or do I need to find just regular 80w90 if there is just that without the gl-5 numbering, thanks in advance I just don't want to hurt anything.