How do you fill differential 98 Tahoe?

There should be a plug (either 3/8 or 1/2 inch plug threaded into differential housing) on differential facing rear of vehicle. You can use a socket wrench (3/8 or 1/2 inch drive) with a small extension to remove plug. Place your finger inside and if there is no oil you must fill until it is at the level of the plug. Refer to owners manual for proper type of oil.