Does a 99 GMC Sierra 4x4 need to have the front wheel bearings packed?

If 4X4 Check Outer CV Joint On Right-- Or Housing Bearing-- If 4X2 Check R/H Wheel Bearings

Sounds like you need a front axle actuator. This actuator bolts to the side of the front differential housing. It is electrically engaged. You can purchase them online starting at about $40

FRONT END SHIMMY AND SHAKING COULD HAVE A TIRE OUT OF BALANCELOOSE OR WORN WHEEL BEARINGS, WORN OUT BALL JOINTS,WORN OUT TIE ROD ENDS, FRONT END NEED ALIGNMENT.BRAKE ROTOR WORN OUT OR WARPED, MANY THINGS WILL CAUSE FRONT END TO SHAKE SHIMMY.

your wheel bearings are gone

the bearing hub is a pre-assembled unit it has to be pressed together and the bearings have to be preloaded that is why you can only buy the hub assy. and it a whole lot easier to replace then the old 4X4 ft. wheel bearings.HAVE FUN

the leak is probably a separate issue from the noise. is the leak very bad? can you tell if it's engine oil or transmission lube/fluid? most likely the rear main bearing seal needs replacing. the noise is most likely the clutch release bearing. you should replace all components of the clutch assembly which include; clutch plate, pressure plate, release bearing and piolot bearing. also have the fly wheel resurfaced. while the trans is out, you can check the rear main seal and the trans input shaft seal and replace accordingly.

you could have problems in the shift control module.or faulty switch in dash.

if the only problem was stuck in 4x4 would not be huge deal. You could just pull the driveshaft off the front. But with it stuck in low range not sure that you can get away with doing that.

wheels bearings? loose ball joints?

Check front axle actuator see if it came unpluged