i dont think its ever a good idea to let 10 year old fluid ride if you wiliing to change it
did it change for the better or worse? if it changed for the better it could of been bad.
It does not have a timing belt, Chevy did not use timing belts in there truck engines.
I have a 2001, and after a oil change and slight tune up i get about 20.5 hwy and 15-16 city.
Should be changed every 60,000.
It does not have a timing belt, It has a chain and it don't need changed.
Timing belts are changed at a set mileage which is listed in your owners manual. The belt may look good and be ready to break. Change it when that manufacture tells you to change it.
As long as it is running, & starting good, & getting good mileage, change them at 100,000 miles.
At the same interval you changed it the first time.
The manufacturer recommends that the timing belt be changed at 90,000 miles. == ==
The shaft inside the trans will have to be changed it is longer in a 2 wheel drive and the taIL SHAFT.
You cannot know by looking at it. This is why the belt is changed at a set mileage as listed in your owners manual. You change it when your vehicle reaches that mileage. You did not list make, model, & year so I cannot tell you the mileage at which it should be changed. Warning: If your engine is an interference engine and the belt breaks you will have serious engine damage.
View your owner's manual for specifics on the mileage requirements for maintenance. My rule of thumb is to change the belts when you change your spark plug wires and your cap and rotor.