Many thanks for the quick reply!
The wheels will eventually never get seen, as the station I've built hides them all with platforms, so I'll try swapping them out and see if that helps (I went for technic axels as it was just cheaper than buying wheel sets!)
I'll also check the version number on my receiver, just in case that is a factor.
I'm no electrical expert, but I did some mooching last night and it also seems the AMPS you get from a 9V is less than 6 x 1.5's - AND the different types of 9V (Alkaline or ZInc-Carbon etc) also give out different AMPS, so yours may well just be better batteries than mine. - I'll buy a nice Duracell instead of Tesco own brand!
Thanks again, and as you know about the wheels I used, I guess you watched the video, so thanks for that too!
Best wishes
Jez