HAVE A 1999 GMC SIERRA 1500 WONT MOVE IN FOWARD OF REVERSE

may be you should make a diagnostic and you can do it in a garage or you can do it by yourself if you want to do it by yourself you need some tools and you can find some good ones here: spobd2.com

unfortunately what it sounds like is the transfer case like you suspect. inside are bearings and gears and a chain what happens is the chain will stretch and cause this problem it will actually jump the teeth on the gears, you will need to have the chain replaced in the transfer case. sorry to have to tell you this but i hope it helps.

If noise is come from front end, and your truck is not moving at a stand still, it's going to be your ball joint's, bad news, if there OE there will be no grease fitting. New ones will come with grease fitting for future lube jobs on ball joint's.

Replace the gasket between the air manifold and the CFI.

Not safe to drive. Sun shell broke or stripped out. Does it have all 4 foward gears? If so you have a different problem. Still in trans though.

check under truck drivers side at transmission linkage may need an adjustment or is binding--

check fluid levels change trans fluid and filter

Your sun gear shell (google it) has broken in your transmission. I'm guessing you only have 1st and 3rd forward gears? I have a 98 Z-71 and have been through 3 of them. The OEM shell is junk. When you take it to the tranmission shop, tell them to replace it with a hardened shell. My local transmission shop charged about $450 (parts and labor) to change the shell only. The very first time it broke (about 65,000 miles) they went ahead and rebuilt the tranny while they had it apart. If you've never had your tranny rebuilt, I reccomend doing it while they have it apart - they probably will, too. I have the advantage of knowing my mechanic since I was born (small town). He is as honest as they come and this was his suggestion.
Since he put the hardened shell in mine, I have had no problems.

Good luck!

Pull the starter out and bring it in to the auto parts store to get it tested