93 4x4 pickup

I have a 93 4x4 and when I drive it in 4x4 hi it tends to lurch or slip. Anyone have any idea what might cause this? I haven't checked to see if it does it in 4 low becasue I live in DC now and don't have anywhere to use it. Thanks.

hey mine does the same thing on a dry hiway only tho, if ya figure it out let me know [email protected]