I have a bad vibration that comes from my gear shift and also makes a small squelling noise. I drive a 1999 chevy S-10 4x4 v-6 pickup.

Check the gear lube in the transmission. It may be low.

Could you be more specific. Exactly when does the vibration happen? How long has it been doing it. Is there any sound related to it. Does it seem to come from any specific area? Does it seem to be in the searing wheel, shifter ??? Auto or manual transmission?

In addition to what BK recommended, try driving in 4th and see if the vibration and squeal still exists. If this has the T-5 transmission it uses tapered roller bearings on the input and output shafts, rollers on the nose of the output shaft, and a needle thrust bearing between the shafts. If any of these bearings start to fail the shafts begin to wander fore and aft and the shafts will climb due to loss of bearing preload. 4th being a direct gear unloads these bearings so you can differentiate these bearings from something in the transfer case. But check the oil level as movement of the input shaft destroys the input shaft seal and oil leaks out of the front fast.