New tyres....

I have a 2003 325Ci Sport, 24K miles.
I had new rear tyres put on about a month ago, after the originals were worn to about 2mm, the fronts still have 4mm on them. I have Dunlop SP9000s all
round, 225/40/18 front and 255/35/18 rear. I've done about 1K miles on the new tyres.
I now seem to have a couple of issues:
a. on tight motorway slip road, and fast corners at speeds of 60+ mph, the DSC light flickers and the DSC intervenes where previously I've had no issue. The result of the DSC intervention feels unnerving.
b. the car now wanders at speed, requiring constant correction.
This isn't usual and not how I remember it - is this solely due to the new tyres or is there coincidentally another problem ?
I didn't have the tracking done with the new tyres as there was no sign of uneven wear - would this help ?I'm pretty sure by now the tyre release coating would have worn off, so does anyone have any other ideas. Is the DSC caused by the slight differences in tyre diameters ? I've thought about replacing the fronts to see if that helps, but they've still got some life.
At the moment the beemer drives worse than girlies Pug 307 :-(
Rob.
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I've got a 330ci sport with the same size wheels as you and am now on my second set of Dunlop SP9000's and have been very pleased with them. I've never had the problems you describe. I'd go back to the place you had them fitted and ask them to check them out.
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I have P6000s on the front of my E46 and cheapo GT Radials on the back, no such issues here.
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