You could run synthetic 5W-30 in it. A lot of guys have done that and are having quite a bit of success with it. Personally when I did my transmission I put AMSOIL Torque Drive in both.Hi, I pulled my transfercase to re-seal the seam, and wanted to change to synthetic, just not sure what to put back in. It's an NP1 with electronic shift, gm only recommends Manual transmision and transfercase fluid, but what do the rest of you run for synthetic? Thanks.