Fluid Replacement Schedule

Can anyone provide a good reason why differential and Tranny fluid needs to be changed at the "GM" intervals. Is there a need? Or is this just a way for GM and other Oil change shops to generate revenue. I find it very hard to believe that with todays engine/vehicle technology and the types of lubrication being produced for longevity that these sort of fluid replacement recommendations are even valid. I can get behind oil changes every 3-5k miles but after normal driving and no towing I can't fathom why I would need to pay for 300.00 worth of fluid and labor charges for those fluid changes. Keep in mind that price includes oil and cooling system fluids too. Im also even skeptical about the cooling system fluid change too. TIA - All Opinions Apprecitated!! Thanks

As far as the tranny fluid goes, it loses its resistance to heat as it gets older meaning your tranny will run hotter and hotter. Plus, the filter in the tranny will get full of metal shavings that naturally wear off gears and clutches so the filter needs to get changed. The differential oil is also more exposed to abrasive wear with the metal shavings that gradually wear off the gears. Don't let anybody sell you a transmission "flush" because the filter won't get changed. Make sure they just drop the pan, change the filter and refill it with fluid. Hope this changes your mind a bit.