If your animation appears to be sliding, then you just need to adjust the values between movement speed and animation speed so that they match up. Either slow down or speed up you object, or lengthen/shorten your animation frames.
Look at how many pixels your character's foot moves in a single loop, and make sure that your character moves roughly the same amount in the same timeframe. The simplest way to do this is through trial and error - test different values until you find one that works. To save compilation time, you could tie the movement speed to some keys and adjust it on the fly, then input your final values after testing.
Of course, if your character has acceleration and deceleration, there will always be a point when the feet don't match the motion. In game maker I would fix this by tying the animation speed to the movement speed, but I'm not sure if that's possible in Construct. You could fake it by having two animations - run and walk - and switch between them when you hit a certain speed.