Let me start by saying that I have never animated in 3d but the same principles apply to 2d and classical animation. If your character is sliding, then move the last key-frame closer or further from the original position. Try until you get it right, if you can't, then your walk cycle might not be done correctly.

To avoid sliding the feet have to move exactly the same distance between each (key)frame. You have to have a guide line on the ground and do the walk cycle accordingly. If the distance the foot travels between each key-frame varies then the final effect would be the sliding you describe. Look here, at the bottom of the page is a blue dude walking on the floor-grid I described.. if you were to move him from point a to point be, you'd have a perfect walk cycle - zero sliding.

https://minyos.its.rmit.edu.au/aim/a_...e_project.html

hope that helps