Scotty,
I drive a 2009 Toyota Sienna with 130,000 miles, and a 2010 GMC Yukon with 175,000 miles.
The books guidelines for cleaning fluids (tranny, coolant, brake, steering) has LONG time intervals based on mileage to change fluids.
Here in Minnesota we have cold winters, and I do all city driving with our cars.
With the age and mileage of my cars, I plan on doing “drain and fill on all my fluids every two years from now on.
Do you think that is smart or a waste of money?
It makes no sense at all to use the same interval for all fluids. They serve different functions.
A better idea would be to shorten the intervals in the manual by, lets says, 30%.
Your GMC manual should already provide a "severe" maintenance schedule which would work well for you.
This makes sense, but the “severe” maintenance records only go up to 150k. The vehicle has 180k now.
so if it's 50k miles between changes (or whatever it is) just carry that on ....