Hi Flying Geezer

I'm sure you able to do a proper setup but have you looked and checked the following:
1 - Ensure swash plate is level
2 - Ensure trims are centre (sub-trim and trims or Tx face)
3 - Ensure fly bar is centred and paddles are aligned

It appears to me like you have either trims or a non level swash because of heli wanting to slide that much on spool up. Once in a hover, what does the heli do if you leave the cyclic stick? I would say that during your pitch setup you've compensated with your links for the skew swash. If it's not this, then the only other thing I can think of is for you to try a different set of main blades. They might be balanced and everything but maybe one flexes more at higher rpm than the other.

Regards,
Gavin