it will be fine...i'm not exactly sure if you can only get the 3.92's in the 9.25 do you know if yours in the 8.25 or 9.25 because thats what you need to know the difference between on the 80 or 75

Don't know, the owners manual says 80w-90

should be fine either way since once its warm its a 90 weight anyways

I recently switched to Amsoil severe gear 75w-140 when i rebuilt my 8.25 rr, i dont do much towing, but like the extra protection