My son just bought a GMC Sierra 1500 4x4 with 200,000 miles on it and wants to change all of the fluids.I downloaded an owners manual and it and it showed to use 75w-90 synthetic oil gm#89021677 superseded by 88900401 which is about $45 a quart,is
there something in the aftermarket that is cheaper that can be used? The RPO code is G80 limited slip,does a limited slip additive
still have to be added like the older models used?Thanks for any help.

 

i used 80w-90 from vavoline...the additive is your prefference...some guys swear by it...some guys say not needed