I have a loud clunking noise in front end of my 99 silverado when i engage 4wd

Wow. A snapped side shaft sounds serious. If you lift the front end of the truck, (or the rear end for that matter) the wheels will appear to be counter rotating, it is the way a differential works. If you turn the left wheel forward, the right wheel will turn backwards, and vice versa.
When you change to 4wd the front end does make a rather loud clunking sound as the gears engage. You should therefore change while the truck is stationary, then slowly move forward or back until the 4wd engages, then take off.
If your truck went OK on ice, it should go as well on pavement, just don't try to engage 4x4 while moving.

check the actuator vacuum/ wires for operation as it sounds like the actuation is not completing the movement properly for the front hubs.

Does the driveshaft for the front wheels turn when in 4wd? The actuater might work but the diff lock for the front wheels might have broken. If the front driveshaft does not turn when in 4wd, the transfer case might be the problem.

I don't think you will know whats going on until someone takes the transfer case apart. It could be the shifter stuck in mid position and it is not completely in either position.

Sounds like your axle seals have leaked out all the fluid. Take it to a garage and get a free estimate on it and they will check your axle seals.

chec fluid in transfer case and also the front differential--git a haynes book at a parts place for procedure

probaly dont have a problem your truck probaly has a gas engaged 4 wheel dr modual and what you hear is the gas modual engaging

It is somewhat Normal Depending on how Loud the Clunking is. This is a Common Complaint on the Chevy 4x4's. I have verified this through the Dealerships here in Oklahoma and they all say the Same thing But, I am with you, They should go into 4x4 without that Clunk for as much as we pay for them.

Yeah i get the same thing when im hitting the whoops at 80 miles an hour.What is the deal with this.

My 2003 F150 Supercrew would not engage in 4x4, it ended up being the shifting fork in the front end, cost me $200.