My 2003 2500HD manual calls for 80W-90 in the front axle and 75W-90 in the rear axle. Is there a synthetic lube that is approved by GM which I could use in both axles?
You can use synthetic in both. Look in the TSBs and you will see one on the front diff where you need to change the vent cap if you go with synthetic due to a compatibility issue with the materials.
Kid:I bought a Mitsubishi Fuso truck for my business a few years back and it came with the 140w gear oil. The truck came from California and the service manual stated that the heavier weight was for year round sustained hot climates(100 plus deg) and heavy loads. I know this is an apple and oranges comparison but the same may hold true for our trucks.I'm sticking with the 75-90w mobil 1 synthetic.
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