Hi, decided to save my friends 89 3.0L 5speed Dodge Raider from the junkyard...has over 388K kms on it and a few rust issues around the wheel arches. I will be doing the basics first...full tune-up, fluids, brakes, suspension, and some minor body work and fender flares.

The factory service manual recommends GL4 or higher for transfer case and manual trans, and GL5 or higher for the front and rear diffs (LSD additive for rear diff required). The temp index in the manual recommends 80W90 down to -23C, but i want an all season oil that goes down to -35C or so. My question is, i was going to go with 75W140 synthetic GL5 in both diffs, transfer case, and transmission. Then i saw a post here yesterday that someone said to only use GL4 in the 1st gen transfer cases or transmissions? Isn't GL5 better?