don't have those problems, but for 3s something that might help is to grab later, after the 180, grab, spot your landing and release late ....
and if you're throwing them more corked then regular, you should be happy about that :)
for the scissoring, try to stand balanced on the rail, everyone says you need to lean forward, but if you're having trouble dipping your tip or tail on the front ski, you might be leaning a little too much forward, try a stance where your weight is distributed evenly over both feet, scissoring came naturally once i had a good stance on rails ....
(btw everytime i use the word scissoring a certain image pops up in my head :(, we should name it differently)
and last, hopping on "street" rails (thats how we call rails/boxes you cannot simply ride onto ....)
in the beginning, try stepping onto it.
i read you slide left forward, so i assume you ride on from the left side ?
what you do when you're on the little ramp, lift your right foot(inside/back foot) and place it onto the rail, then do a little hop and immediately place your left foot in front...
i know this sounds kinda weird but it works very well, you're basically stepping onto the rail the same way you would step on it when you would be wearing shoes, one foot at a time ...
then later you can smoothen it out by doing it all in a single smooth hop, then shortening the delay between bringing up the first ski and the second ski, until you hop on with both feet simultaneously ...
i hope i was of some help, i'm not such a legend myself, but those things definately helped me :)
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