Synthetic blend rear diff fluid?

[00Silverado4x4]

So the truck has needed a rear diff fluid change for a while. 90k miles and never been done, yup probably overdue. Anyway, went to all usual parts store places & the ONLY fluid around was 75w-90 synthetic blend? So I went with it, job went almost too easy.

Bolts came right out (presoaked with penetrating oil).

Gasket remains came right off, new gasket scraper finally had a job.

Minimal mess (personal first).

Reassembly was done in first shot.

 

Took it around the block a few times, no noise or leaks. Took it for a cruise around town with the family. Still no noises or leaks. So now I'm just concerned if this blend will be ok with the rear end/G80 or am soon to be breaking something? Don't want to "test" the G80 for a few more miles until everything has "broke in" the new fluid. Just hope I didn't mess up using this blend. What do you all think?

[RyanbabZ71]

Duplicate topic. No need for the same post in multiple locations, this one is being closed. See the maintenance thread for the "open" topic