There is no "access hole to drain the fluid from the torque converter on the 4L60E tranny in the 1999 Tahoe.Here are the instructions from the GM Service Manual:
Automatic Transmission Fluid and Filter Replacement
Raise the vehicle.
Place a drain pan under the transmission oil pan. Remove the oil pan drain plug.
Remove the oil pan bolts. Remove the oil pan. Remove the gasket. Remove the magnet.
Remove the oil filter.
Remove the filter neck seal.
The transmission oil pan gasket is reusable.
Inspect the gasket and replace as needed.
Clean the transmission case and the oil pan gasket surfaces with solvent.
Air dry the transmission case and surfaces.
Install the filter neck seal.
Install the oil filter.
Install the oil pan gasket to the pan.
Install the magnet into the bottom of the pan.
Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application.
Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure.
Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener.
Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.
Install the oil pan to the transmission with seventeen bolts.
Tighten the oil pan bolts to 11 N·m (97 lb in).
Apply a small amount of sealant GM P/N 12346004 to the treads of the drain plug. Install the oil pan drain plug.
Tighten the oil pan drain plug to 18 N·m (13 lb ft). Install 5 Quarts Dexron® VI Automatic Transmission Fluid.
Lower the vehicle.