Jezp,
- check your chassis tweak, make sure its flat.
- try use a thicker front diff oil, like 300000. Or better yet a spool.
- You mentioned you are using foam 37tyres, most of us are using rubber tyres. this might be the main cause of your problem. Are you using foam tyres meant for Nitro cars? if yes, are you using the 26mm front foam tyres in the rear?