Sorry guys, I'm running the KO PROPO EX-5UR the sets that come with 2 receivers. So not RTR.
I have tried 4 different analogue servos with no luck on both cars.
I was running a 27mhz AM setup on my F1 car and it worked perfectly. The only reason I got this radio setup was a built a Pro10 car with a brushless setup and it said not to use 27mhz AM setup with the brushless system.

But I have had nothing but issues.

My mate runs the same radio system, so I will try his transmiter on my cars, but that's not going to be for a while.