You should have your transmission fluid checked every time you get an oil changed. If you have a sealed transmission with no dipstick fluid should be changed every 100k miles. Check your owner's manual under maintenance to see what your schedule says.
You should check your Owner*s Manual to be sure, or if you can't find it give your local Chevy dealer a call. Most cars is every 60,000 miles (for an automatic transmission).
〉 Answered on Mar 2nd, 2008 by Jennifer Frey, Automotive Service Writer and Technician at AskPatty.com