In other words I changed both at the same interval.

I'm changing my rear diff tomorrow with Royal Purple Maxgear 75W90.
The store I shop at carried every redline oil except the gear oil.
Anyone used this with no ill effects? Just want to make sure I'm using the right product and there isn't some other royal purple oil they didn't carry I should use instead. The staff were no help. It says it has a friction modifier built in.

If its not a GL-5 oil then go return it and order your diff oil from the website.

it's GL5 I made sure of that. Says it's for front and rear diffs too.

Should be good to go then.

I drove my car when it belonged to my dad at a track and the diff started binding after only one session. When I bought it from him I changed the diff oil to Redline 75w90 and did another track event with no issues at all. I plan on upgrading the VLSD at some point as well but while I have it stock I'll stay with Redline 75w90.

Interesting post I just stumbled upon. The 2014 service manual states 20K mile diff oil changes.