Silverado 3500, GL4+ in rear end?

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Nov 23, 2020
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I have an '03 Silverado 3500 dually. 11.5" AAM rear end. I changed the fluid back in march, and hadn't really thought much about it until recently when looking at other fluids while ordering (I own a repair shop). I stock a bunch of LiquiMoly gear oils, and I've come to realize I've purchased both their 75W-90 GL5, and their 75W-90 GL4+ (GL4/GL5). Should I be concerned that I might have put the GL4+ in my rear end? Will it cause any issues, considering it still covers the GL5 rating? Only anecdote to offer is after towing, I can smell the gear oil, probably out of the vent. No leaks.
 
If it were my vehicle I would change the fluid to a known GL-5 product in the specified viscosity grade. GL-5 oils are specifically for hypoid gear sets and require an extreme pressure lubricant. If you're unsure what you have in there then I would drain and fill with a known product.
 
I wouldn't worry about it, GL-4+ should be fine, it should really be GL-5 fluid with extra additives to be less problematic with cuprous metals in manual transmissions.
 
They’re interchangeable for differentials. As long as it had a limited slip additive assuming your truck needed one, that’s all I’d worry about if it was mine.
 
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