truck transfer case and differential service intervals

[Keith Hughes]

Tow vehicle question (please delete if not allowed): We tow our 2021 Montana 3121RL rig with a 2021 GMC Sierra 2500 Diesel 4WD truck. This is the first time we’ve owned a truck and want to keep it properly serviced. The truck will be 3 years old later this month and nearing 30,000 miles of which 13,000 are towing miles. The owner’s manual recommends the transfer case fluid be changed every 45,000 miles but there is no mention of if/when to change the front and rear differential fluid. The dealer is recommending both differentials and the transfer case be serviced every 30,000 miles. I’m inclined to go with the owner’s manual maintenance schedule but am concerned that it is silent on if/when to service the differentials. Thoughts and recommendations?? TIA!