Thanks Bill,
Its a med-high grip asphalt track with a few bumps.
New tyres don't fix it.
I realise it could be a million things but as this is something that has just started happening with the same setup and track it makes me wonder if it has something to do with the new diff or drive shafts, or maybe the steering linkage is hitting the toe block.
I'll be testing these out but I was wondering if anyone had similar issues.
thanks again
Dave