Hesitation at distance

[Arronb]

Hi Guys

Wondering if anyone can shed any light on something for me.

I've got a RTR ZX5 which so far has bene great apart from one slight niggle. When I purchased it from Modelsport the ESC was buggered and after 3 weeks I still had not received a replacement, finally Modelsport called to say that they had been authorised to send me another ESC but did not have any stock Kyosho ones to hand so sent me out IIRC an Asman racing one. When it arrived all looked good and it was fully waterproof which was an added bonus.

Now ever since I been using the car from say 20 meters away if I try to accelerate the car judders and hesitates a fair bit before it gets on the move, once going (usually towards me) it seems fine and this problem does not seem to happen when at close quarters.

Now I'm assuming that its the strength of the signal between the aerial from the ESC and my controller, controller aerial is fully extended and cars aeriel goes straight up through the tube and down again.

Anyone got any ideas as its a little annoying and would like to know if I'd be better off with the stocj Kyosho ESC rather than what I have?

Thanks in advance
Arron