I have a used 2003 Silverado and am wondering what I should do to keep it in tip-top shape. It has 85,000 miles on it. Next time I go to my mechanic I plan on getting new brake pads, an oil change, and the transmission fluid changed. Should I change the fluid in the rear axle (I have the G80 locking differential)? Is there any other fluid I should change or regular maintenance I should perform?