7K miles on the factory fill? There are many trucks that never change the diff oil and have 250K plus. I would have at least waited to 100K. This just sounds like overkill.
Welcome to BITOG. There is a MASSIVE AMOUNT of "over maintenance" going on here. I towed a 5,500 pound travel trailer all over the country in my Silverado 5.3-6 speed transmission. At 50,000 miles (the vast majority of those miles were towing) I changed both my transmission fluid and differential. Both still visually looked good.
So yea-your right.