Hello, these are not easy. Did you get the bolts in the pan that are under the access plugs? Here are instructions right out of the GM service manual. Thanks
Important: The low oil level sensor is not reusable. Use a NEW low oil sensor.
Notice: Any time the transmission and the engine oil pan are off of the engine at the same time, install the transmission before the oil pan. This is to allow for the proper oil pan alignment. Failure to achieve the correct oil pan alignment can result in transmission failure.
Important: Always install a NEW oil pan gasket.The oil pan gasket and oil pan must be installed and the fasteners tightened while the adhesive is still wet to the touch.
Important: The oil pan alignment must always be flush or forward no more than 0.3 mm (0.011 in) from the rear face of the engine block.
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.
Tighten Tighten the oil pan bolts to 25 N·m (18 lb ft).
Tighten Tighten the oil pan drain plug to 25 N·m (18 lb ft).
Tighten Tighten the engine oil level sensor to 13 N·m (115 lb in).
Tighten Tighten the transmission to the oil pan bolts to 47 N·m (35 lb ft).
Tighten Tighten the bracket stud to 9 N·m (80 lb in).
Tighten Tighten the hose clip bolt to 10 N·m (88 lb in).
Tighten Tighten the transmission cover bolts to 12 N·m (106 lb in).