You must check your vehicle's specifications or a reliable repair manual for the correct capacity. The owner's manual might list it, or you can find a manual online specific to your Tahoe's VIN or axle configuration. Failing that, a parts store can usually look up the information for you based on your VIN.
Guessing the capacity could lead to underfilling or overfilling, both of which can damage your differential. Always refer to the correct specifications.