Sometimes they like to stick to the gasket and hold on for dear life. Try prying it very gently with a pry tool away from the engine. Below are the removal/installation instructions, ensure you have removed everything that is needed.
Disconnect the negative battery cable. Raise the vehicle, support it safely, and drain the engine oil.
On 1996-98 models, remove the engine oil dipstick.
Remove the underbody protection shield to access the axle bolts.
Remove the transmission oil cooler line bracket from the oil pan, if equipped (on models with automatic transmission only).
Remove the front propeller shaft.
On 1996-98 models, unfasten the front axle two right side bolts and nuts, one upper bolt and nut. Rotate the drive axle forward and turn the front wheels to the left.
Remove the exhaust pipe crossover.
On 1996-98 models, remove the torque converter cover (on models with automatic transmission).
Oil cooler lines from the oil pan and from the adapter, if equipped.
Oil filter and oil filter adapter, if equipped.
Remove the oil pan bolts, nuts and reinforcements.
Remove the oil pan and gaskets
((Oil pan bolt/stud tightening sequence-1996-98 4.3L models))
Thoroughly clean all gasket surfaces and install a new gasket.
Apply a suitable sealant such as GM part number 12346192 or its equivalent to the front cover-to-block joint and to the rear crankshaft seal-to-block joint. Apply the sealant about 1 inch (25mm) in both directions from each of the four corners.
Install the oil pan and new gaskets.
Install the oil pan bolts, nuts and reinforcements.
On 1996-98 models, tighten the oil pan nuts and bolts to 18 ft. lbs. (25 Nm).
Install the transmission oil cooler line bracket (on models with automatic transmission).
Install oil filter adapter, oil cooler and the oil filter.
Install the flywheel/torque converter cover.
Install the underbody protection shields.
If removed, install the starter.
Install the exhaust crossover pipe.
Install the strut rods at the flywheel cover, if removed.
Install the front drive axle.
Install the front propeller shaft.
Install the underbody shields.
Connect the negative battery cable.
Fill the crankcase.