[MJN]

Originally Posted by Alex V.

That page appears to be out of a Chilton's or Haynes repair manual - not sure I'd trust that over factory info.

I've had GL5 in my Suburban's NP435 for the last 7 years and it doesn't seem to be hurting it much, but there is credence to the GL4 argument. My local Napa keeps Sta-Lube GL4, but outside of that I'd just order some online. Very possibly cheaper that way, too.

This page is definitely not out of a Chilton or Haynes manual, try following the link I provided in my original post and you'll find the factory manuals in pdf form and this exact page. In fact, I'll post it again straight out of the 1971 Chevrolet Truck 10-30 Chassis Service manual for your convenience.