I thought it was just my imagination but I confirmed it at the weekend, the power steering on my 2015 Cforce X8 looses sensitivity/power after about 40kph, it is fine on slower speeds or in rough stuff but as you speed up it gets so bad you have a job to steer it, it's like its almost pushing back at you, I have almost ran off the road because of it. Anyone else experienced this or heard of it?

I have a 2014 and it works great at all speeds.

I believe the power steering is designed to become less sensitive at higher speeds.  Steering effort is greatly reduced at higher speed.  I could be wrong but that's my understanding.  The power steering control unit has a speed input from the ECU to control sensitivity.

I thought it was just my imagination but I confirmed it at the weekend, the power steering on my 2015 Cforce X8 looses sensitivity/power after about 40kph, it is fine on slower speeds or in rough stuff but as you speed up it gets so bad you have a job to steer it, it's like its almost pushing back at you, I have almost ran off the road because of it. Anyone else experienced this or heard of it?

Generally, speed-sensitive power steering is by design.  I can't speak to whether or not CF Moto designed it this way, but I would think (and hope that they did).

When you're travelling at lower speeds more input from the EPS unit is helpful because turning the tires at no/low speed is more difficult.  As you're travelling at faster speeds it should require less effort and not as much EPS input is needed.  It's also a safety feature so that someone doesn't get too much input from the EPS at high speed causing a rollover.

That's not to say you don't have a potential issue, but generally at higher speeds an EPS system is programmed to decrease its sensitivity.

[2015 Z Force 800 53/Trail EPS]

If it's locking-up or fighting you as the speed increases, it has a controller problem and needs replaced. Do this before the main unit becomes damaged.

Mine works good at all speeds. I believe it does give less assist at higher speeds like most brands do, but it's not noticeable.