I'm about to order some rear end fluid for my truck and I wanna know what weight to use and do I need to buy any type of special addative for the G80 so it still some what lock up? I'm going with Royal Purple by the way.

 

75W-90 should do it, IIRC...no additive needed for the G80.

 

75w90 is correct

 

The rear diff is synthetic from the factory, and no additive is needed for the G80. (75-90 as mentioned above)