S3 Petrol - 1st gear and reverse shudder after 30 minutes

Having now had the gearbox refurbished and fitted with new clutch and preassure plate, plus new slave cylinder I finally have some notchy, but consistent gear changing. At xmas, I replaced the whole ignition system. However, after 30 minutes of driving, I get a shudder at low revs either at initial take off or in reverse. Having been through the forum, I believe this could be contamination on the new clutch - which, may have happened with the chassis covered in waxoyl and the tightness of the slave cylinder fit (crack case seal all good). Would you just continue to drive it - on the basis it will burn off, or could this be an ignition timing issue (looked all good last night) Any thoughts or input greratly received.

Check gear box and engine mounts are secure.
Clutch should be treated gently for awhile to allow it to bed into flywheel, ie no rapid gear changes and bring the pedal up before increase in the revs.

Thanks for the reply. I checked the timing last night and it was well-out. I think this is exacerbating matters, with surging of power (!) when in low revs and pulling off. I set the timing spot on before pulling the gearbox out, so dunnow how this could have failed so quickly - everything is new, including an autospark dizzy (could not find a duecellar for love nor money).

Thanks again Blackburn.